I always have a drink or two (or three...) when I'm playing. It helps me loosen up and have more fun. I've realized that I tend to do better if I'm genuinely enjoying myself.
I also drink when I play. It just doesn't seem the same when I play while I'm sober. Of course I always have to be careful never to overdo it because I tend to become overconfident when I drink too much and I end up losing money.