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.
A PVC pipe cap.
I was making a lightsaber for my kid, and bought a length of clear PVC from Home Depot. (I know, they have bad politics, but Lowe’s didn’t carry clear PVC.) My local store didn’t have any clear PVC or clear accessories in stock, so I had to place an order for shipping, so I got a couple things “just in case” for the build. One of those was a pipe cap.
Didn’t end up using the pipe cap, because lightsabers don’t have that sort of end. It now sits at my desk as a teeny tiny trash can. Bits of thread from sewing, nail clippings, tags I clip off of shirts, a lot of things fit in the teeny tiny trash can. When it’s full, I empty it into the trash, but for a rather small pipe cap, it holds quite a bit of small trash.