I'm able to find many of the things I need for my Airbnb apartment at Doillar Tree (stores are everywhere in the U.S.). Everything there is $1. I can get cleaning supplies, bathroom supplies like body wash, shampoo, lotions, etc. Plus, I have a basket with things like extra toothbrushes, deodorant, razors, etc. etc. I ask guests to take anything like the toothbrushes or deodorant or something that is "personal" with them when they leave. Dollar Tree also has frozen food so you can get frozen pancakes, waffles, frozen fruit and other breakfast items to put in the freezer. My Dollar Tree has bagels, cream cheese, milk, coffee, syrup and condiments - all of which I have stocked in the cabinet for my guests.
If you stock more than one Airbnb, DollarTree.com will let you buy in bulk. You have to get at least 12 of any one item. Normally, the shipping cost is $4.95, but they sometimes run specials where they have free shipping. I'm not sure, but I think you can pick up the order in the store without having to pay for shipping.
Hope this is helpful.