I bought a pair of USB heated gloves for a couple of dollars, they have 2 removable heating pads.
They will run all night on my Jumpstarter battery pack with built in USB socket.
Or you can just buy the heating pads on their own, but they cost more than the gloves.
So all up it costs around $50 including the jumpstarter.
http://dx.com/p/usb-heated-warm-glov...ted-pair-30366