After searching around for an hour I couldn't find very much information on the subject of item respawning. Well, there's a bit of information on how long it takes a cell to reset (conflicting though it may be) but there isn't very much information on what items respawn when a cell is reset. So I did a little bit of testing and here are the results.

The method I used to test this was to make a small mod that changed the game settings iHoursToRespawnCell and iHoursToRespawnCellCleared to 1. I would go inside a cell, do something, leave, wait a couple of hours using the T command, purge the cell buffer with the pcb console command, then go back inside to see the results.

First off, I could find nothing that would ever respawn inside of a player home. Not even food and plants. I'm sure the reason for this is so the player can decorate without having to worry about their stuff being knocked around by respawning items.

I haven't tested any dungeon interiors but I did test a mine and an inn.

All of the random items I grabbed off of counters and such would respawn after the cell reset. This included an iron pot, some produce, planted items, a woodcutter's axe, some steel bars and some loose iron ore. I think it's safe to assume that all mundane items will respawn after a cell resets. More testing needs to be done to see how far this extends but I think as long as it's not a unique or quest related item it will respawn.

Items dropped from the player's inventory would not despawn after the cell reset.

I also checked to see if leaving and going back inside before the cell had the opportunity to reset would affect how long a cell has to reset. Just like in Oblivion when you enter a cell the reset timer gets... reset. So whenever you go inside a building that you've been inside before just keep in mind that it will be another thirty days before the items you looted earlier will respawn.

Ore veins are a little quirky about resetting. The appropriate time will pass and you'll go in, it will look like it's ready to mine but you won't get the option. Leaving and going back inside seems to fix it. This could be a bug associated with setting the reset timer so low. Also ores seem to reset on their own little timers disassociated with the cell they're in. This means they don't reset when the cell resets but thirty days after the player has mined them regardless of how often the player visits the cell. I haven't tested it but I think this may apply to plants as well.

Well that's all I got for now. Use this info for whatever. If you're making a player home in the CK with a garden or something I recommend putting the garden in a different cell and leaving the player home tag or whatever it is off. Otherwise if you're worried the world is going to run out of something because you pick it up off a shelf then don't. It will most likely be there after a month.