Here's what I would do:
My first option would to be make my own soda...(I already do)
You can be ghetto about it too, you don't need to invest in some machine unless you really want to.
I simply purchase carbonated water (jarritos mineral water) and then I add in my own flavoring. Personally, I don't mind the sugar or calories, but I know there are some calorie free flavorings that you could try.
Lately I've been doing vanilla blueberry...it's slammin!
My second option, would be to just get rid of carbonated beverages and go towards tea. Iced tea is refreshing, you have tons of options as far as what to make it from. I'm currently using chaga, reishi and chamomile. You can add lemon/lime to taste, and if you really need a sweetener with no calories, try stevia with it.
There's also agua frescas, which can rack up the calories pretty quick if you aren't careful. But look into Jamaica (hibiscus) and tamarindo (tamarind) those two are delicious, and can be made relatively low-calorie/calorie free.
My final option, would be to find a nice tasting BCAA to sip on when you're thirsty.