First, grab some sponges. Then, get a big bowl of water and soak the sponges until they are full of water. Place each sponge in a small zip-lock bag. These bags keep the liquid from spilling when the ice melts, and they let the sponge refreeze when you stick it back in the freezer. All you have to do now is freeze these bags overnight, and they can be used as ice packs the next day. Make the ice pack once, and keep using it over and over again!