What is something really stupid you purchased that turned out far better than expected?
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.
Not my purchase per se, but my grandmother bought me some knives made by some french company that i didnt think id use too much. Turns out their great for smaller things that my ka-bar is a bit excessive for.
They have a good rep and long legacy, the original fancy picnic pocket knife. More of a gentle slicer than anything, but they're dirt cheap and easy to mod.