Stage fright is something you learn to deal with as you play for people -- there's no way to get around it other than playing for people and going through it as much as possible.

I know a lot of singers who'll have a beer before a show to relax their vocal cords, but generally, depending on alcohol or other "party favors" to help you with your jitters is a very bad idea.

Personally, as much as I may drink after I'm done playing, I drink as little as possible before and durring the gig.