You can make reusable ice packs with some liquid dish soap, water, and a hand towel/big towel and some type of ziplock bag; though the vacuum seal food bags are much more reliable.

The dish soap allows it to remain pliable so it can be molded into you. And the custom sizes and shapes allow you to place it usefully- big flat ones on the spine is ooo-la-la. If you need to cool off in a hurry? Long ones under the arm pits, shins, fore arms and around thighs, too.

Easy change is a longer, some what wide shape that you can fold around your neck, kinda like a scarf.