I use the gel packs you freeze and are used for shipping things that need to be kept cool. They are better than ice packs because they don't have condensation or leak. They're cheap, too.

Polar Tech TP12/MS Ice Brix... https://www.amazon.com/dp/B007PB3IB0?ref=ppx_pop_mob_ap_share

They're reusable. I keep some in the freezer all the time. The cold really helps my migraines too