A few years ago I bought (on line) a pair of folding prescription glasses in a very small package (smaller than an altoids tin). The glasses were cheap (under $20), rugged and well protected in their hard case. They were the perfect backup glasses for carry. Like CrookedKnife, I use old regular glasses in the car and desk. You have to be careful of heat molded frames in the car though. I had several pair of GI glasses and sunglasses that I kept in various cars only to find them warped when I tried to use them. I am trying to find the site for the folding ones or something similar and will let you know when I find it.

Respectfully,

Jerry