For me, it really depends on where I'm playing. Generally, however, I must admit that i'm so wired after a gig that I like to have maybe two beers after packing up, etc. back at home with the band because otherwise I stay up all night thinking of different ways I could have soloed, thinking over the songs endlessly, etc.
Often I won't drink anything, it's more the ability to have a quiet chat with the band, and to "chill" a little. Occaisionally I've smoked a bit of a joint, but it's so rare that I have any interest in touching the stuff, usually because I hate the feeling of trying to read or write and knowing that I am a little stoned. I know why so many musicians do it though, it can be great at relaxing yourself, but that's why it's so dangerous, because it can seem so nice.
"Dozens of people spontaneously combust each year, it's just not that widely reported".