If you go on P3 during the cruise, just try to make good choices of lean meats and veggies while there.
Try to fill up on low carb veggies – the fiber in them will help you feel fuller so that you won’t eat as many calories. Try not to eat much calorie dense foods for the first 2 weeks of P3 like nuts or cheese.
And when it comes to vegetables, think in terms of things like steamed broccoli and such – salads can be okay but in some cases are not the best choice because the lettuce is really not filling, and the dressing is typically a lot of calories, so that you can finish a salad like that and not feel satiated- whereas the fiber and density of the steamed vegetables will actually fill you up, for very few calories.
Lastly, how far into P3 you are when you go on the cruise will make a difference in what you can get away with. If you are the beginning in Week 1, I would advise being very strict. If you are in Week 3, it’s possible that you may get away with a glass of wine here and there if you are careful about the other things you are eating.
I hope this helps!