I just made a bunch of Gel packs from a pair of Orex pants, some boric acid, and a vacuum sealer.
Orex makes disposable clothing used in hospitals and nuclear power plants. The stuff disolves in boiling water. If you take a pair of the pants, put them in a big cook pot and add a gallon of hot water you can melt them. Just turn on the heat and bring them to a boil. After about ten minutes and a little stirring, all that is left is a little thread. You can toss the thread out.
Cool in down with a bunch of ice to near room temperature.
Disolve 8 tablespoons of 20 muleteam borax into 2 cups of water. Zap it in the microwave and disolve as much as possible. Stir this into the melted pants. It will gel up and turn into the product sold as "slime".
Dump as much as needed into a vacuum bag, put it on your vacuum sealer and suck & seal. Toss it in the freezer and you are ready.
Of course you won't be able to resist playing with the stuff.
Try it!