I had a pair of Ray Bans that went to pieces when I started backpacking with them. Since then I buy 20-30 dollar pairs, including a pair of glacier glasses, which are too dark for driving (warning sticker on them tells you not to use them for that). Been through quite a few that have been scratched, broken, or just lost. I don't carry a second pair backpacking but keep a spare in the glove box.