When DMing I try to stick to water (I need something to keep my throat from drying out, but don't want to get drunk or hopped up on sugar or caffeine, or end up making endless trips to the bathroom). Depending on circumstances I might mix in some coffee, soda, or 1 or 2 beers (especially if we're combining a meal -- lunch or dinner -- with the play-session). As a player, I'm more relaxed so all bets are off. I'd probably drink Tequila shots at the game table if someone was offering. As kids we drank tons of soda -- 2-liter bottles of Coke, Mt. Dew, Mello Yello, and Nesbitt's Strawberry soda -- which, combined with mounds of chocolate Little Debbie cakes and Tootsie Rolls and M&Ms got us so wired we couldn't help but stay up all night. Nowadays even the thought of all that sugar is making me a little queasy...