It;s a vacation, people, not a beauty pagent! If you feel that you need to lose weight, lose it for the benefits of better health you will gain, but not because you are going on a cruise. That is a lofty goal and a great motivator, but can also set you up for less of enjoyment on your cruise because you wanted to be 50 pounds less, but are only 20 pounds less.
My husband always returns from a cruise at least 5-10 pounds less than when we boarded and he stuffs his gullet every chance he can get. But then, he is very active while on board, usually far more active then on land. And every night at midnight he's moaning over his bloated stomach, but at 3am I can always find him at the pizza bar.
For me, its all about variety and moderation. Regardless of my vacation destination, I have very specific rules for eating. First, I never eat or drink anything I can get at home. For example: hamburgers, hot dogs, chicken noodle soup, etc. Or a drink like a rum and coke. Those are things that are accessible to me any time. I'm on a cruise, I'm on an adventure, so I'm going to eat adventurous things, like every appetizer and a cheese plate instead of broasted chicken or top sirloin or even a field green salad. I'll get a DOD in a souvenier glass, of course or have fish at dinner (hubby can't stand the smell of fish in the house) or anything else that is a rare treat that I either don't have access to at home, or its too expensive at home to enjoy. And of course, everything in moderation. You don't have to clean your plate, you don't have to eat all of your food. If something tastes particularly delish to you, go ahead and order a second helping, but just eat a bite or two of the starch and don't eat the bread (as wonderful as it is, it takes up too much room in the stomach).
So, once you set foot on that ship, the only diet you should be on is the see food diet, but that doesn't mean that you are going to return 15 pounds heavier. Eat small meals, eat frequently and don't eat things you can get at home. Now, everybody knows I'm not a burger kind of gal to begin with, buy Guy's burgers sound interesting enough to try at least half of one. I'll do tea (because I really do like little sandwhiches, not the big, regular ones) and I really would rather make an entire meal of appetizers. But I'm not going to let my weight, overabundance that it is, dictate my vacation.
Lose weight for you and you alone, have a goal of being healthier when you go and when you do, enjoy all that a cruise has to offer in moderation.