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.
If you ever break or have surgery on any part of your arm, you'll be very happy to have that cape in the winter. I have a couple from when I broke my wrist and used them again when I had shoulder surgery.