The ice packs in first aid kits degrade pretty quickly too. Ours failed after cleaning and bandaging my friends thumb that he almost cut off at the first joint. But we were able to get him stabilized and to a hospital within about an hour or so. He kept his thumb although it was a little questionable when it doubled as a pez dispenser. I am glad I got it cleaned and wrapped before his wife could see it. Thankfully, she only saw it after the stitching. Otherwise, she would have freaked...even more.

I would suspect hand warmers would go bad too, but have never used one here.