I like to carry a "hypothermia kit" of sorts in my hunting pack.
This consists of a sit pad, a cover of some sort, usually a poncho, but could be a space or sportsmans blanket, and a heat source, which so far has been an extra 1/2 dozen hand warmers, that get tucked in my pits and strapped to my Carotid arteries with a neck gaiter. The hand warmers will warm you up, but wont help you dry out.
I carry a can of Sterno when there's a possibility of immersion, but am a bit sketched out by curling up with an open flame when I've got a case of the cold stupids.
I have a tealight lantern that seems safe enough, but was not useful in subzero temps as only a small amount of wax would melt around the wick. I assume the aluminum cup was radiating the heat out of the wax before it could melt. I'm pretty sure its a "Uco Micro candle lantern", but its in the bottom of the POS crate so I cant confirm at the moment.
I have an old Zippo hand warmer, that I've played with, but its not really the kind of thing that I want leave in a pack "just in case" and messing with flammable and evaporate liquids when cold dumb and clumsy doesn't appeal.
I'd appreciate any suggestions, towards a practical heat source that I can justify always carrying in a Tarahumara based hunting kit.