I've been on one traditional cruise before and I had lost 75 lbs prior to that. I've also always abhorred buffets so that part wasn't a challenge for me. I think the idea that you don't get seconds, maybe eat half an appetizer/half dessert and possibly half meal might work for you?
I kept pretty active on the cruise I went on and lost weight when I got back home.
If you are paleo, I'm guessing you are low carbing? If so, don't touch a scale for a week or so after you get back.
You can't out-exercise poor eating habits.