However, in the spirit of things, assuming this is not a troll, I will contribute a couple things.
One is bicycle inner tubes. I use them for various things.
They keep metal sling swivels on rifles from squeaking.
I use them when a scope cap (like the POS butler creeks) are a shade too big. You can cut a band, and slide it over the objective lense, then slide the cap over it, to make it tight. It also works to put the cap on, then slide one over the cap, to help keep it in place.
If you look at the below pic, I have one inner tube band under the front cap, and one over the rear cap, helping keep them in place: