Have anyone tried sodium acetate heat packs? They are clear until you click a metal thingie (yeah, that's technical) inside the bag and then it reacts, crystallizing the sodium acetate and giving off heat (130 degrees F).
I was curious how long the heat lasts before recharging (boiling the bag in water until it turns clear again).
Are they worth getting? I was thinking this could be a nice addition to my emergency kit.