I keep spare contacts and solution in my Jeep through the heat of summer and freezing of winter, and haven't detected any issues. I do rotate them every six months, either through need or as part of standard kit maintenance. I also have spare distance and reading glasses in the car.

This is also true of my EDC, GHB and BOB, though minus the distance glasses in the former two.

BTW, Zenni Optical is a good source for cheap, spare eyeglasses. I bring all my prescription glasses and my sunglasses with me on my annual eye checkup, and get them refitted. Since I buy the contacts and an occasional distance glasses from him, he has no problem adjusting them for me. Most of the eyeglass chains will do the same for free.