I've seen tennis players take a swig of water and a mouthful of banana between games. IIRC, bananas are high in potassium. I suppose you could take a tiny pinch of seasalt, too.
Basically, I'd have thought skip the drinks and have water and just a little something to eat with it.
Alternatively, Sally Fallon's Nourishing Traditions has got recipes for a number of lactic-fermented beverages in it:
Those might be worth trying, if you're game for the work of making them. They apparently have plenty of mineral ions in them, and they have lactobacilli, which are good for the gut. She says they were traditional drinks for people doing physical work in several parts of the world, and if that's so I suppose they'll have proved themselves over time.