These chemical hand warmers are very common among outdoorsmen. They basically expose iron to air and moisture to create an exothermic reaction (heat). After all warming stops, they're meant to be disposable. In a bad situation, you can spread some of the pack's contents on a wad of cotton or natural fiber (yucca, hemp, jute...) roll into a "cigar" and, with speed and pressure, create an ember to set your camp fire.
