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.
Considering I got 3 years worth at about $1.50 a month, I get more than enough content every month to make the cost worthwhile. I don't use it much for privacy but I use it a lot to access movies and such.