I've gone through a lot of ice lately. Finally a few weekends ago we broke down and went to the drug store to get an ice pack. My sandwich bags were leaking all over the place and sitting on a bunch of ice cubes in a pool of water isn't the most comfy. What we found were $20 ice packs. Ha! Thanks but no thanks!
Instead we got some decent ziplock bags and alcohol. We figured if we could lower the freezing point of water we could make some stellar ice packs ourselves. You could use salt too! We got home and mixed 3 parts water with 1 part alcohol and let the ice packs freeze over night.
Let me just tell you, they are rockin' awesome. They don't freeze completely solid, which makes it nice to bend around my hip. Also, lowering the freezing point means that this ice pack is COLD. Real cold. And it stays cold a lot longer. Make sure you wrap it up in a towel first because that sucker will stick to your skin. So if you're ever in need of some ice packs try it out, it works great and is slightly less than $20 :)