www.creationkit.com.

http://www.creationkit.com/AddItem_-_ObjectReference
http://www.creationkit.com/RemoveAllItems_-_ObjectReference
http://www.creationkit.com/RemoveItem_-_ObjectReference
http://www.creationkit.com/OnLoad_-_ObjectReference
Simple: create a leveled item list with the items to add, remove any items you want (or all items), and add the leveled list of items (make sure it has the use all flag). Set the event OnLoad(), or something similar.
http://www.creationkit.com/ObjectReference_Script
Using something like this;
http://www.creationkit.com/OnUpdateGameTime_-_Form
or this;
http://www.creationkit.com/OnUpdate_-_Form
You could register the script for updates, and have it update periodically however you'd like with new items, and use a check in the event to make sure the initial OnLoad only occurs once.
If you are lost here - start with the papyrus primer and tutorials to get ya started.

Look at other scripts for examples after you've done that, and try to piece together how stuff is done.
I could probably write the script, it's not too complex, but I think it'd be better in the long run if you figured it out - it'll be that step in to figuring out how to do more with it.
Here's some examples of two of my scripts;
http://dl.dropbox.com/u/56852942/cleanUpIS.psc
http://dl.dropbox.com/u/56852942/varietyScriptSize.psc