Floors, carpets, stairs, your feet, a bicycle, maybe even your car, dirt, gotta invest in good walkable dirt, uhhh, what else here... socks, probably chairs, ladders, flights, if you're flying always invest a lot in it, uhhhh. yeah probably some other stuff.
I dunno I guess the point of my joke is that I think this is one of those heuristics, or like, general expressions, that ends up taking longer to say than what it actually means. "invest in your shoes and bed" takes longer to say than "invest in anything that keeps you off the ground".