?
drink water?


It probably doesn't matter what you drink.
In saying that, however, the time control of the game should be considered. For example, if you're playing blitz, a lot of caffeine will likely be slightly benificial, unless you have some abnormal reaciton to caffeine.
In a long time control game/tournament, however, a large amount of caffeine will benefit you at first, but many people experience a caffeine crash, which may slightly affect your play.
I bet GM's (like Carlsen) bring the same drink to every game out of ritual, or to simply stay hydrated. It would be naive of us assume that what you drink otb would drastically affect how you play.

Soda is poison.
i completely agree. in fact, i never ever ever drink anything except water

Small amounts of caffeine are good for athletes, but I have idea if it would be good for chess. I'm pretty sure eating isn't good before a game though.
in real life FM eric told me that a bannana is good for chess play
Also soda makes you better at first but then you get a caffine crash and thats not good for chess

There is of course another approach to this dilemma ...
My kind of game....plus, seeing this on the board assures there will not be a draw due to 50 moves with no pieces taken!! (or, is it, pieces drank?)

Caffine helps in chess but 2 much sugar causes crashes whitch detroy the endgame
so i think no coke but coffee unsweetened

At the beginning of every OTB game, offer your opponent a nice, cold, sugar-based 20-ounce bottle of Coke and hope that he accepts it. Ha! Why stop there? Offer him a 2-liter bottle!

Mountain Dew has more sugar & caffeine
A dubious honor, for sure. These days, I really try to avoid sugar as much as possible. I'm now convinced that sugar is addictive and that excessive sugar consumption is a chronic toxin to the liver.
Water is fine, and a little (no sugar) coffee or tea is okay. Caffeine *is* slightly addictive, but I don't think it's toxic.
