All the bars and in the dining room (your bar server will have to get it). In the Windjammer, if you can find a bar server, they can get you a soda. You can get a special cup when you sign up for the drink package. If you don't want to hassle with that, you can just show them your sticker when you order a soda.
There is coffee, tea, water, some type of juice or lemonade or punch available in the Windjammer and at the drink stations free of charge. The soda package is not good for a canned beverage.