It really depends on the type of site it is, like for an equine sim you'll need bags of feed, tack, treats, grooming tools, and general food items like apples and carrots.
Fantasy gets a little tricky, but you can't go wrong with different foods, even make up your own foods, which I've seen personally you're really good with!
Something my games need is things you'll find hidden in the woods, like sticks, acorns, pinecones, stones, minerals, small animals.
These are just ideas to get your imagination going. I don't know for sure what's most needed out there, but I wish you the best of luck!