Water Only
I'm just starting out on my WLS journey, but I can tell you one thing I'm grateful for is that I've never been a big soda drinker. I drink unsweetened iced tea. And my favorite are the herbal flavored teas, like peppermint and peach, that are already decaffeinated. You can also get plain decaf tea, but in summer especially, I like the flavors. :) My suggested brand that's available in just about any big grocery store would be Celestial Seasonings, but there are lots of others.