Just got back on the Sun, 7 nights. We purchased a soda plan for $28 - they give you a little Coca-Cola thermos thing that you can request to have refilled limitlessly at any of the bars during the cruise. They also put a little Coca-Cola sticker on your cruise card, so if you show that to any of the waiters they will bring you a soda without charge. (Good to know so that you're not carrying a big tacky thermos into the dining rooms.) I'm not sure how much they charge for the same plan on cruises that are shorter or longer.