The 2 L bottles would not fit in your fridge in the cabin. My suggestion. Get a note from your doctor stating that you are diabetic and that you cannot drink alcohol and only allowed Diet Canada Dry and Diet Fresca. Then bring a few cans of each with you. Princess is pretty accommodating. We bring a couple of cases of water Nestle and they never object to water and we have brought on 6 cans of Diet Coke previously and never had an issue. But if they were to confiscate these cans from us, it would be no hardship for us. But if you are diabetic, you do not want to drink the diet 7 up that is on the ship because it is very carbonated and comes from the bar fountain.