Pop...yankee. Just kidding!
I drink sweet tea. Yes I know it's empty calories, but considering I eat very little fried food and absolutely no dairy products (think about everything I can't eat) I figure I'm entitled to something nutritionally naughty. If I find myself gaining weight I switch to unsweet for a while.
Another option is Propel water. That stuff tastes awesome and has only 30 calories per bottle. I almost can't work out w/o some. It hydrates like water w/o giving you the empty sloshy feeling.