Well, since it's the winter time, it's like.. one of those things that the Japanese have everywhere xD Like a heating pad that lasts for a few hours that you break something in it or activate it when you want to use it :p
/dies
I WANT EVERYTHING
Edit: I think it might be kind of like this one:
'A truly magnificent invention from Japan, this is a wonderful little cloth bag that gets hot when you open the plastic wrapping. It gets hot, stays hot and is a wonderful way to warm up if you're cold. Since it can fit in your pocket, it's perfect for sports, skiing, or any time when you feel cold and just can't warm up. Measures 3.5 x 4.5 inches and comes in this handy pack of 10 warming pads. Peter has loved these ever since he came to Japan, and every time he gives them as gifts to friends back home, they are overjoyed. Each pack contains four individually wrapped hot pockets. Brought to you by Hakugen, the top brand in Japan. These extra-large warming pads last for up to 16 hours, and are recommended for heavy-duty warming in cold environments. '
Edit2: LOL I just looked at it again and it's like.. this bag of a liquid that has a little piece of this metal or something in it [we looked at this kind of thing in Chemistry] and it reacts with the liquid when it is released by pushing a 'button' in the package. You can see it on the picture there. It's reusable too when you boil it and stuff. It's so cool xD
/dies