One of our friends showed us these hand warmers so we bought some today in preparation for our New Zealand trip. They are clear packs of goo (sodium acetate) and when you snap the metal disk inside they turn into crystals and get hot. I find them very exciting. To reset, you just boil them for 5 minutes. And, the best part is that the were one sale for buy 1 get 2 free (and 2 per pack, so we have 6!). I love a sale. See the awesome video here.