When I worked in a restaurant kitchen, we used to soak rags with water and freeze them in the walk in freezer, then once it’s nice and frozen we’d wear the rag around our necks.

There’s large blood vessels in the neck feeding your brain, so if you’re able to cool down the blood there, it’ll spread to the whole body surprisingly fast.

I actually managed to get cold in hot humid july summer in the kitchen with that method.