the person who told me about alcohol/water in a zip lock bag for ice packs. (Did you like my click bait! :)) I'm almost certain it was someone on this board!
At the beginning of the year I splurge on my budget a little and get reusable ones, but by this time in the school year they've all mysteriously disappeared.
The rubbing alcohol and water "ice packs" are my go-to, and they're perfect!