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.
I bought like 10 of these at Habitat for Humanity and gave them out during a fly outbreak. Some of the neighbors looked at me weird (granted it was the first time I met them) but I'll swear by these things. I hate killing bugs but sometimes you gotta do what you gotta do.