I bought a piece of 1.5 inch stiff foam to try to fix a sag in a bed. It didn’t work but having that thick piece of solid foam around has been a life saver.
Need something flat to put a laptop on? Throw it on the foam. Going to be doing something that requires you to be on your knees for a while? Get the foam!
It went from stupid purchase to something I’d gladly replace if it broke.
Small adhesive rubber bumpers or “feet” that came in a variety of sizes to put on the bottom of things. Was under $5 but has brought me some joy going around my home putting feet on anything that isn’t level or could scratch or makes noise. Something oddly satisfying about it.
Similarly, the felt version of this. Nice for if you need to move something, ie furniture (we have wood floors).
I did this too, everything had feet by the time I finished. Everything.
Also great for any doors (cupboard or otherwise) that can bang the wall when opening. Especially the ones where the hinge makes it open with some force. Just find the place where it makes contact with the wall (often the handle, but it depends on your setup) and put the bumper on the wall in that spot.