Hydrate yourself. I can't tell you how many times I've had to yell for water on stage because I forgot to bring some up there before hand. cold beer is good for a while, but you'll want WATER for damn sure. Course I sweat like cheese in the sun, though.
ANother thing,, cords. Make sure your cords are long enough to handle a big stage. Our fist gig was on a big ass stage, and my amp-to-pedal cords were too short so I had to turn around for every patch change for that show. That little shit turns into problems if you play out alot.
Ah good call I need to buy new cords...mine are shoddy as hell.