That was sort of the loose redneck idea, use what I have to make a backup lens. Thankfully I've never outright needed to use it, but if I ever lose my glasses, I sleep with my wallet in my pocket, with my backup lens right there.

Edit: And yes, the lens comes from a slightly dated prescription of mine, plus the lens seems pretty darn scratch resistant, so it's a solid emergency lens, should I ever need it.