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!
I'm not much of a soft drink person so I wasn't paying very close attention; but I don't recall seeing any caffeine-free diet drinks. I know they had Coke products, and as Krysta stated, Diet Coke; but no caffeine-free diet sodas. Sprite has no caffeine but they don't carry the diet variety.
A friend of mine drinks only caffeine-free Diet Coke and he always takes his own, except when he cruises Crystal. They actually lay up a supply for him when he asks in advance. Now that's what I call service!
I never thought about bringing my own soda...it would help cut down costs (and assure you have your favorite drink) but how would you transport it? Would the cruise ship take it away if they spotted it in your carry on? I would be afraid the cans would explode in checked luggage (I guess this is really only an issue if you are flying to a port I guesss.) What is your plan?
I never take my own--like I said, I don't drink much soda. But those that have to fly just pick some up at a convenience store in route to the ship. Most lines allow a "reasonable" amount, whatever that is. You should check with the line to determine their exact policy.
Thanks for the good answers. I am not trying to save money, just to have available what I can drink. I cannot drink alcoholic beverages at all, and no caffeine, so I do rely on caffeine free soda. Since we live in San Diego and are cruising from LA, flying is not an issue. I just plan to bring six cans, and then will pick up six more somewhere in Hawaii for the return portion on the Regal.
The only caffeine free sodas I've found on Princess is Sprite. The Sun did have diet Sprite in a couple of the bars last year, but not all. I had some on the Lido deck and in the casino lounge. I didn't see any caffeine free diet coke or dr. pepper either. Best wishes!