COMPCOOLER Backpack ICE Water Cooling System Hoodie Cooling T-shirt 3.0 L Flow Control

Incredibly effective

I tried this one recently and the difference wearing it vs not was night and day. Full disclosure, I'm wearing this to keep cool inside of a stuffy costume, and this seriously allows me to do whatever I want in there for 3 hours in relative comfort. Do note if you're using ice cubes the time is halved, but this is an amazing all-in-one solution for cooling yourself down for whatever situation calls for it.