These gel ice packs are really cheap to make. If you want them more moldable then use 90% rubbing alcohol for a more solid one that is still pliable use 70% rubbing alcohol. Both work the same as far as cold goes so it’s just a matter of preference.

What you need:

1 quart or 1 gallon plastic freezer bags (depending on how large you want the cold pack)
2 cups water
1 cup rubbing alcohol
Instructions:

Fill the plastic freezer bag with 1 cup of rubbing alcohol and 2 cups of water.
Try to get as much air out of the freezer bag before sealing it shut.
Place the bag and its contents inside a second freezer bag to contain any leakage.
Leave the bag in the freezer for at least an hour.
When it’s ready, place a towel between the gel pack and bare skin to avoid burning the skin.