Hotshotz Hand Warmer.  The 3x5 is great as a hand warmer, in pockets, under beanies, and works great for massaging that special someone!
The 3x5 lasts about an hour depending on how well you insulate it. Hotshotz work instantly, are portable, reusable, non-toxic and MADE IN THE USA.  Press and release the button to heat the pack. Follow the directions in the Tech Specs to boil the heat pack for re-activation.

Tech Specs

There is an activator button in the Hotshotz heat pack. Firmly click and release it with your thumb. The heat pack will instantly crystallize and heat up to 130 degrees. The heat pack will slowly cool and become solid. Then make it ready to use again: boil a pot of water with a cloth at the bottom. Place the solid heat pack in the pot of boiling water and simmer for about 5-8 minutes for the hand warmers. Once all the crystals have melted in the heat pack, allow it to cool to room temperature. The heat pack is ready to activate again.