On the pickle juice thread, where consensus seemed to be that acids help reduce cramping, someone suggested switchel, an old summer drink that farmers used to drink in very hot weather.

To one pint of water, I add 2 T of apple cider vinegar (Braggs), 1 T of molasses, 1-2 t of powdered ginger, and a pinch of salt. I think it's delicious, and it seems to help a bit with the heat and cramps.

I also make a sports drink with 2 T of lemon juice (which contains a lot of potassium), 1 T of sweetener (we have bees, so I often use honey), and a pinch of salt--but the switchel tastes better.