Instant hand warmers are great--just shake 'em up, and you've got spontaneous warmth to thaw your hands during the cold winter months. But they're awfully expensive, and not because they're complicated to manufacture. In fact, you can make them yourself in a few very easy steps.
Calcium chloride ice-melt pellets
Two ziploc bags of different sizes
1. Fill a large ziplock bag one quarter of the way full with calcium chloride ice-melt pellets (available at most hardware stores).
2. Fill a smaller ziplock bag halfway with water, close tight, and place inside the first bag.
3. Squeeze the smaller bag until it breaks open, to create a heat-producing reaction that will last 20 to 60 minutes.