Anyhoo, I thought I'd share mine here too, with a picture.
If you use mason jars for canning or storage, the red lids from peanut butter jars fit them perfectly. So after you open your jar of jam you don't have to muck around with a sticky lid and band. It's only the red lids but seems to work for any brand I've saved them from.
I learned this from my grandpa who would not have called it a "life-changing canning hack!" He would have found that term totally asinine. He would have called it common sense. Of course I think he saved every single jar lid that ever entered that house, so sooner or later one was bound to fit.