You are ALLOWED to use purchased items for building your builds in Kitely or any other OpenSim grid, including private non-public grids, local offline grids or any other grids run on OpenSimulator technology.

You are ALLOWED to use the purchased items for commercial builds like clubs, shops, malls etc.

You are ALLOWED to use purchased items for your avatars only. You can export it and use with different avatar names in other grid.

You are NOT ALLOWED to give away any items or part of the items to other people, to avatar who are used by other people than you or avatar who are shared by multiple real life persons.

You are NOT ALLOWED sell, give away for free or for reward, or give away as prize any of purchased items or the part of items, regardless if parts are original or modified by you. This possibility is not allowed by setting of permissions – all my items are NO TRANSFER.

You are NOT ALLOWED to make any derivative works based on purchased items by any possible way, now known or hereafter developed. Derivative work means, among other things, to take a detailed picture of my items or their parts and use it as part of your product, or any other author’s work, or to copy feature of my items, like size, prim torture, sculpties, meshes or other features and make a new copy based on these features.

You are ALLOWED make photos, capture an image, make videos and machinima where my items are used and displayed.

You are NOT ALLOWED to change permissions or author of any purchased items. Every permission changing of items or parts of items is violation of this EULA.

You are NOT ALLOWED to export the items outside of OpenSim grids, to desktop application or any other environment now known or hereafter developed.

You are NOT ALLOWED to use any purchased items or their parts in any grid, world, game, medium, software, hardware, formula or product owned or partially owned by Linden Lab Inc. in any format now known or hereafter developed.

You are NOT ALLOWED to purchase any item made by Zuza Ritt or sold by 21strom store in any OpenSim grid or online e-shop intended for OpenSim grids, if you are or you will be the employee of Linden Lab Inc. If you even think about to be Linden Lab employee, do not buy my items. This rule is unlimited, worldwide and irrevocable, you cannot revoke you purchases later, you cannot be refund, you just will simply violate these terms and you will be punished for it.

If you are not sure about your intended usage, feel free to contact me
If you find any items in any grids or worlds, and you are not sure if there are genuine work by me or illegal copies, please let me know.

Thank you for your purchases and for respecting IP rights.

Good solution is make backup from SL and restore it on your home local OpenSim standalone region, you can use vanilla OpenSim, Diva Distro or Sim-on-a-stick, all are free to use, or New World Studio with several editions (I have not tried this option).
Make new region, where you restore all your products, that is your main copy of your content, you can backup your region with your precious content as you need.
Make the OAR file from this region, import it to the new world, pick up all your products and use them. Thanks to Isis Ophelia for discussing this brilliant idea;)

In Kitely virtual worlds every registered user can have got one region for free. Region in size 256×256 meters can hold up to 100 000 prims.
You can create new world (1 region) and import OAR file there for free. If you will replace your region by new OAR file later, you need 10 KC (Kitely Credits, cost for 1,000 KC is $5 or less) for importing this new OAR file to Kitely.
If you need categorize and manipulate your object in Kitely, you can use Kitely Merchant Sandbox, which is free to use for unlimited time.

Kitely Market is now free to use, listing fee was canceled at Oct. 5 2013, you can list all your products at Kitely Market for free. Kitely respects your rights and don’t claim ownership over your creations. You can backup all you listings at Kitely Market.
Only fee you pay is for sold product, and it is clear explained at Kitely Market documentation.

Backup with Second Inventory (Stored Inventory)

This app is available at webpage or inworld in Second Life for one-time fee. It is not developed since 2009, there is only community support, and there are some problems with backup. Anyway, if you have hundreds or thousands items to backup, it is still best option. You need to buy MultiAvatar version.
Second Inventory (SI) looks like light non-graphic Viewer, it is intuitive to use.
You need some calm place in SL, when you can stand for hours, like skybox on your parcel.
For restoring you need a place, where you can rez items – your local OpenSim or Kitely Merchant Sandbox in Kitely is the place. You will rez items and wear items, when restoring wearables.
You can backup whole folder in SI, so move all your products in one folder and start backup. It could take several hours to backup hundreds of items.
You cannot backup coalesced objects. You can backup linked objects and single items – prims, textures, scripts, sounds, animations…
You can only backup items, which you created and you have full perms for the object. Object inworld does not need be set for fullperm, but you have to have these permissions for it. Due SL restrictions you cannot backup full perm sculpties, meshes or scripts bought from other authors for your products.
There are bugs in SL, like some of your object, made by you, has you as a author when rezzed, but has “Unknown Avatar” as author when in Inventory.  You cannot backup this item, regardless you are genuine author of the item.
It is known bug for several years, LL support is not able to help you with this issue. They have not fixed it yet, you can vote on Jira, that is all you can do with it.
SI is buggy too, there is text log after every backup, check it and if some items are not backuped, make the backup manually for every item.
The biggest pain in SI is fact, you cannot restore the folder. You have to restore one object only at a time.
With proper settings of SI you can restore all your objects to their original folders.

XML export/import

This possibility is known several years, recommended was the Imprudence 1.3 Viewer, which is out of date. I am using Firestorm or Singularity. Firestorm has Export feature hidden by default , you can activate it in Debug Settings:

The best solution is to use same Viewer for backup and for restoring items. Firestorm in OpenSim version could be used for log in into SL.
There are some problems when same cache directory for several grids is used, uploaded textures are missing, because cached items are used for upload. You have to upload all textures separately, including sculpt textures, and apply them on prims again.
Using the several instances of Viewer can help avoid this problem. Make several icons on your desktop, new for every grid, every instance has different directory for cache.
There are same restrictions for backuping content – in SL you can backup only items where you are author. You can backup items, where are the parts from other author (like old huge prims), these parts will be missing after import to new grid.

HPA export/import with Angstorm

I have never tried that one, but due the wiki backup includes scripts and textures.

DAE or OBJ export

There is possibility to export all your objects, including prims and sculpties, into 3D files – OBJ or DAE. You can edit them in 3D applications or import them as mesh in other grids.
Prims and sculpties exported as mesh will not be low-poly meshes, be aware of that fact.
New Singularity 1.8.3 is able to backup textures and/or textures setting (like pattern repeating) with DAE or OBJ files.

Shape export

You can export your avatar shape in Appearance-Shape. Singularity since 1.8.1 is able to that export.

These informations are based on my experiences, that ones I have tried and I am sure it works. If you know another possibilites, or find some mistakes in my explanation, let me know.

If you want to log visitors of your region or parcel to spreadsheet, it is possible even in new Google Drive. This howto is made for spreadsheets in August 2013 and it works properly.
You do not need any special skills like programming or inworld scripting.

1. step

Thanks to Maria Korolov, for the idea and very nice and descriptive article. Her instructions are part one. My howto explaining how to change the Google URL and inworld script to work with current Google forms.
Make your new Google form as described in article, get the form URL.
Read more info about script there, if you want. Download Maria’s script, if you would like to study the changes.

2. step

Bellow is my complete script for your inworld counter. Before you use it, you have to change some parts of script. It is not working as is!

Your current URL for view the form looks like this one:

https://docs.google.com/forms/d/XXXXXXXXXXXXXXXX/viewform

where XXXX… is your unique ID for this form.

You have to change several parts of script:

First line of script – insert your Google form ID above
string google_formkey = "XXXX...."; //MUST REPLACE with your own Google form key

Next part for change is explained by Maria – if you want log in your avatar.
If the owner of inworld object with script has to be logged, comment this line:
//if( llDetectedKey( i ) != llGetOwner() )

If you do not want to log in your avatar, let it uncommented:
if( llDetectedKey( i ) != llGetOwner() )

Tha last part is most tricky.
In my script you can find this line:
string URL = "https://docs.google.com/forms/d/" + google_formkey + "/formResponse" + "?entry.YYY=" + detected_name + "&entry.ZZZ=" + region_name + "&submit=Submit";

All blue parts has to be replaced by your values.
My values above representing this URL:
https://docs.google.com/forms/d/XXXX…/formResponse?entry.724632390=AVATARNAME&entry.57313582=REGIONNAME&submit=Submit

Devide your URL to following parts:
First part is before XXXX… (your unique ID), in my case "https://docs.google.com/forms/d/"
Next is your Google form ID, it is loaded at first line of script in string google_formkey
Add the rest of URL between Form ID and question mark, in my case "/formResponse"
Add ID of your entries. First one starting with question mark (?), other ones starting with ampersand (&)

How to find your entries IDs?
For some reason Google do not use neat entry IDs like “entry.1″ and “entry.2″ anymore, but some random numbers.
You can find it in HTML code of your form. On the form page rightclick on the word “Avatar” and find “Inspect element,” “Show source code” or similar option, depending on your browser. It shows the code and probably highlight the element of “Avatar.” See the picture bellow.
Find the IDs of your elements and replace them in your script – "entry.YYY" by Avatar value and "entry.ZZZ" by Region value.

You can check the correct values even without scripting and logging inworld. Put together your URL with your values:
https://docs.google.com/forms/d/XXXX…/formResponse?entry.724632390=AVATARNAME&entry.57313582=REGIONNAME&submit=Submit

Replace AVATARNAME and REGIONNAME by any values you choose.
Insert URL into your browser and press Enter. If you get error message, you made a mistake. If your URL is right, Google thanks you for submiting your answer and you just manually insert first visitor to your spreadsheet!

Download sample script. Works in OpenSim.
Download Second Life version of script. (Escaped avatar name)

Insert script with proper values to your object inworld. It is done.

I hope this howto will be helpful. If you find very different Google form URL or if it does not work for you (and you are absolutely sure it is not your typo), let me know in discussion.