I installed a camping gear mod that sells them on this brother in IC, but it makes no mention of a Camping Gear Receipt, that is for sale for over 2k gold.

The other things I have noticed are: Well Marker, over 1k gold; a Water Keg, ~200 gold.

I guess some mods install some extra things...I remember a mod saying something about a trashcan, which is for sale on this guy, but I have no idea why I would have one and / or place one.

I'd assume those are all from your mod.

Save the trashcan, which is in my game too. It's from COBL, I think?

Yep, those are all modded. No idea which, but definitely not vanilla.

So many readme files...so many mods...

They are from FF_Real Thirst.

^ What Petrus said. The trash can is Cobl; everything else you mentioned is FF_RealThirst. The camping gear, etc. makes it easier to stay away from civilization for extended periods, if that's your thing. The well marker can be used to sink a new well. You might want that if, for example, you install and use a non-Cobl-aware home. The trash can can be used to permanently get rid of items, including zero-price items that you otherwise cannot sell; you get some, for example, with many house upgrades, and may not want to simply throw them in the river. You should find these items on many general merchants across Cyrodiil.