Some years back Calumet either sold or used as a promotion a plastic 8x10 gray card. It seemed like a clever idea and I cut mine into smaller more manageable pieces. I keep them in my camera bags just in case. On an early fall trip to Yellowstone one evening it was really freezing and early the next morning the windshield was frosted - it came in very handy as an ice scraper. (as well as the original intention with my spot meter - measure twice, expose once)