cramp buster bev
If it's just normally hot I'll drink only lots of water, sometimes with a squeeze of lemon and some ice.
Second level of heat (85 - 90) I'll drink water and coconut water; more water than coconut. Sometimes I'll eat a bite or two of banana for the potassium.
But I'm a huge "sweater". Once it gets summertime in FL, I will get heat cramps after 2-1/2 hours or so, losing several liters of water that pours down my legs in rivers - I sweat like Andy Roddick! (Cramps are not, as is commonly thought, a "lack of conditioning". Many super-fit pros suffer from cramps during a long match.) So I consulted a fitness expert and he told me to take potassium and magnesium tablets before I play (of course I always hydrate heavily with pure water); then I bring along the following home-made sports drink:
1 liter filtered water
2 TBL orange juice
1/2 to one full tsp salt
ice to cool it down
I alternate this with lots of plain water. If you don't like salty water, take a salt tablet after the first set or so. I have found that this keeps my energy up and keeps the cramps away 100% - because the problem with sweating isn't so much you're losing water, you're losing MINERALS. Plain water isn't enough to keep your mineral balance healthy, and even if you don't cramp, you'll start to feel tired, and feel heat exhaustion without supplemental minerals (also known as 'electrolytes').
Gatorade and PowerAde also work in an emergency, but they're full of sugar and artificial colors/flavoring/preservatives - so not healthy in the long term; and they don't have enough minerals to do much good anyway.