Fucking everything, to the point it's a problem. I replaced my windscreen wipers the other day, when I broke them to fit them in the trash can, I kept the thin metal strip that is inside and acts like a spring. I don't know if it's spring steel, but it sure is spring-y and you never know when they may come in handy.
I've got a box of boxes, all different sizes, cause you never know!, as well a bag of ziplock bags, there's got to be like 400 of them.
As a techie, yes please, we definitely need different points of view