Depending, it'll vary between water, iced tea and <i>potions of tooth decay</i> as the iced-tea drinkers call soda, caffeinated or not.
The most impressive group I had was when I fenced. We'd play Saturday afternoons after fencing class. Everybody would run down to the corner Pizza Hut and get two-liters of Dew or Coke, and that would start us off, and when we wrapped up 'round 9 o'clock or so, we'd had gone through two or three twelve-packs of Coke or Brisk. The stacked cans made a very impressive pyramid, and were, occasionally, used as terrain and/or baddies during combat. (The poor man's hex-map: Tile floor and dice for minis.)