My Husband and I just got off the Sea Princess a week ago (I assume all of the ships have the same sodas...) Sodas (and most drinks) are not included in the cruise fare. The only exception is at the buffet, there is free juice, iced tea and yucky instant type coffee. I think sodas were around $3 each unless you purchased a all-you-care to drink soda sticker for around $25 per person (7 day cruise price.) The only diet soda they had on our ship was diet Coke. One day I requested diet 7 up or diet Sprite and the answer was either "no" or maybe the selection was only available in cans... therefore not included in the all you can drink price. I was too cheap to buy it!