Adhearing to the KISS princeable without reinventing the wheel my suggestion would be a couple lighter fluid type hand warmers. Ive found one inserter into a small pocket stiched into my sleeping bag foot box works wonders sooo I ASSUME where one is good several could be better or may... just qualify as a portable sream bath in some quarters.
"Necessity is the plea for every infringment of human freedom. It is the argument of tyrants and the creed of slaves."
So I haven't clicked all the links here but something you could try (might have been mentioned already) is http://www.omega.com/googlebase/prod...FYVFMgod_AIAeg
Coupled with a fuel cell from http://www.horizonfuelcell.com/store_us.htm could get you through the night quite nicely, but not cheap.
--If a cow laughs hard, does milk come out its nose?