One of my oldest schemes was to make a sort of like russian hat, those high fur ones, and sneak a six pack in there, hooked up to tubes, where you can sneak the tube down to your mouth and drink. For football more where the temperature is colder.

But it could be done with any sort of diaphram. I think military guys carry like a bladder of water, something like that on the belly with loose clothing made to look like you were overweight would work, at least for us skinny people.