You may purchase a "soda card" (not really card, just sticker on your sign and sail card) for about $28.75 (adult). As I said they put a sticker on your card and you also receive an insulated cup (this was on the Dawn). Using either your cup or your card you are entitled to all the soda you want for the voyage. The card is not good for canned soda. It can be used on deck, the lounges, and in the dining rooms (sodas not included in meals). It is a good deal depending on the amount of soda you drink.
It varies by cruise line. You should be able to find it on your cruise web-site. We usually get soda cards for our kids. We also bring on cans of pop and have never had a problam with it. Again, depending on the ship there is usually tea, juice, water, etc., and you can always get juice through room service. (The soda cards can't be used for room service though)
For kids ages 2-17- they can get a soda band= 16.00 for unlimited soda all week long. Juices are usually served at breakfast, and are free, along with coffee, tea or milk. Iced tea is sometimes available. the soda band is mostly meant for kids under the age of 13- but if the seller of the soda band cannot see your kids, then s/he can have it. Bartenders have yet to refuse a kid with a soda band. If over the age of 13- tehy are suuposed to only be allowed to use the "teen passport"- 20 non-alcoholic drinks.
We got the soda cards for our cruise a couple of weeks ago. I bought both the kids cards and the adult cards, and since we drink a lot of soda (no diet pepsi, tho, all they have is coke products) it was well worth it.. it was $16 for the kids, and $28.50 for the adults.