Note: I occasionally stay in my own listings, so some of these are personal observations, as well as comments from guests.
1) Chair pads for my upholstered chairs. Not the ones that tie to the back of the chair, but ones neatly stick to the seat. Purchased after enduring the first permanent, sunscreen-produced stain, these pads have saved my chairs.
2) Wooden knife holder with knives and scissors included. I never realized how useful scissors can be in the kitchen.
3) Multipurpose Oxiclean. Use it for laundry, upholstery stains, tile grout. Magical.
4) Full-length mirrors in the bedrooms.
5) Glass or polyurethane furniture toppers. Tops for dining table, console, end tables, dressers, nightstands still look brand-new after dozens of guests.
I could go on and on, but these are the first “finds” that popped into my head.