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.
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.