I went on a cruise in nov and I'm going on one again in sept. It can be hard if you are trying to stay on plan but you have one of two choice. A- control yourself or B- dont...
to be honest when I went I started off the first 3 days eating on plan and it was fine the buffets had lots of healthy options and even the formal dining halls for dinner had calorie counts and healthy choices on the menus. I told myself I could have what ever I wanted AFTER I ate a full plate of healthy choices first. meaning I had to have a salad, maybe some grilled chicken with veggies and a full glass of water... IF i was still still hungry I had what I wanted. trust me I was so full on good food there was no room left for the bad... the last 3 days of the cruise . I said FUNK it I'm on vacation and I'm going to eat what I want in moderation of course...lol and I did... the great part about a cruise and going off to port is there is soooo many activity's to do. swimming, dancing, mini golf (on carnival cruises at least) that the extra activity I was doin more then made up fro the extra calories I was taking in.
So I guess my point is only you know yourself. If you feel that you need to be strict while on vacation.. then set your mind frame to that and stick to it..
If you feel you can relax a little with your eating habits with out going overboard or with out feeling guilty about it then Hey I say your on vacation live it up an dont regret it!
either way have a blast! I LOVE cruising!