Exercise, less fast food or none at all, more healthy food. Beer isn't what causes people to become fat, it's the urge to eat while you get wasted that makes you fat. So you can continue to drink beer if you drink it, but in moderations of course, don't get wasted on it.
Beer is healthy actually, but with everything else, too much is bad.
Drink water. Try energy drinks? I'll be doing that on Monday's match. Bring a chocolate bar, but it's just a quick burst of energy, won't last long. But it'll help for a few games.
Though seeing as you fatigure after just one game, it sounds like you're really out of shape.
