Dunno if you know this or not, but Wal-Mart sells some sugar free drink stuff..lemonade, peach iced tea, and rasberry ice. You add a packet of the flavoring to a 16.9oz bottle of water. The stuff is great!! Sugar free, sodium free..but tastes wonderful!
You can do the samew thing with Crystal light - they even have small packets that are just right for a water bottle. I use just half the packet as I prefer it diluted.
I'm going to disagree about it having to be decaffeinated. South Beach allows us to have 1 or even 2 cups of caffeinated drinks a day. I drink hot tea myself. I have my first cup of the day with caffeine and then switch to decaffeinated after that.