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.
Hand rolls of stretch wrap. Have an artificial Christmas tree you want to make for back in the box? Wrap that thing up. Have a stack of stuff you want to bind together to move more easily? Wrap it.