pocket warmers - a plastic pocket of a gel like liquid with a small metallic disc that you 'pop' which starts a chemical reaction of sorts (at leat a change of state) from the liquid to a gooey crystal state at the same time realeasing toasty warmth for yer tots ...

They last about 20 mins or so and can then be recharged by boiling them in water until clear again ... mine have lasted years...

this is the first link i found on the net:

http://www.extremedreams.co.uk/catal...roducts_id/150

There are plenty other manufacturers, suspect they are made in bulk and rebranded by whoever wants to market them

i have even wrapped lenses in them when shooting at night to avoid condensation