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.
Unfortunately I think we’re not there yet. My one folds into a meter-long bundle of a metal plank with wheels and a metal pipe and while it;s still light and handy it won’t fit in any backpack.