We all like drinking at gigs, just make sure you don't drink so much you actually forget the gig. Drinking can effect your perception of things, you may think that shouting out is suddenly funny or shoving people when your favourite song starts is acceptable. This obviously depends on the type of gig but in general it is not. Don't get too drunk that you are unnaware of the people around you, there's nothing worse than being stood behind the drunk.
If buying drinks for your friends before the band comes on, take a friend with you...it's not possibly to carry five beers in plastic glasses to the front without it pouring down someones collar.