I don't keep anything at my desk.
throughout the day, I drink a mix of coffee, mountain dew (if it's in stock in the kitchen, otherwise pepsi), and water.
a lot of it depends on how much I'm actually at my desk, though. some days I'll go through 5-6 drinks, and then like today, I've been here for 4 hours and I've gone through 1/4 of a MD.