Maintaining weight on a cruise

I cruise twice a year for 2 weeks at a time... I never gain more than a few pounds and once I'm back to normal routine any gain disappears.
I do practice moderation whilst away but I do eat every meal (I don't DO skipping meals LOL), I keep an eye on my carbs more than usual and walk loads.
Enjoy the trip and you can get back on track when the holiday is over

For you its only 4 days, so its not like you can eat too many calories over your maintenance in that time to gain anything more than a few pounds at worst.

I got back from a cruise less than two weeks ago. Before I went I had lost 65 pounds and thought I wanted to lose 10 more, so I was really worried about coming back from my cruise and having undone several months worth of weight loss work. I thought about this a lot before I left. Some of the strategies I used:

1) I made sure to keep up the habit of 8+ glasses of water per day.

2) Regarding activity:
--I have a Fitbit, and I made sure to get at least 12,000 steps per day.
--I used the stairs exclusively/did not get on an elevator the entire 10 days. If I needed to climb more flights of stairs than I could manage at once, I'd walk up a couple, then walk the ship to the other stair bank and keep climbing.
--Participate in activities that move your body while on the ship. It could be a fitness class or a dance class, whatever you like. If you are used to working out, I suggest continuing to do that onboard.
--When in port, I walked to town (between 1-2 miles each way; most other people took taxis) and for my sightseeing. We were on a budget, so didn't plan any expensive excursions. If you have the money for shore excursions, perhaps you can pick some active ones.
--If your favorite part of cruising is laying on the beach/around the pool, be conscious of the fact that you aren't burning very many calories doing that.

3) Regarding food:
--I decided ahead of time that up to a 3 pound gain would not freak me out because I could lose that again in a month after coming home, but I didn't want to come back 7-10 pounds heavier (a several month setback) so I had to keep some control over my food choices and calorie intake.
--I reminded myself that I want to stay thin more than I want to overindulge on any food they could possibly offer me. Now I'm not saying I didn't try what looked good, but I didn't OVERindulge much.
--I did not feel the need to try everything that was offered. Several things that looked good my husband tried, and I asked him if it was good enough to be worth the calories for me. Or I tried a bite of his and didn't eat the whole serving myself. There were one or two things that were really, really good, so I ate those, but mostly I was happy enough with my choices and didn't go get what he had.
--I ate what I wanted, but only what I REALLY wanted. If there wasn’t anything I REALLY wanted, I made the lowest calorie/highest fiber choice possible (usually fish and lots of vegetables at the buffet at lunch) and saved the extra calories for later when there was something I really wanted (there were some amazing cranberry/white chunk cookies that I ate every day and even stashed in my cabin for the days they didn't have them on the buffet).
--I didn't eat bread before dinner. I love bread, but it is a chunk of calories that I chose to save for something else (usually dessert or a sweet bread the next morning at breakfast).
--For the most part, I didn't eat things that I could make at home. I ate no chicken or pork, but ate a lot of high-quality beef and fish which are expensive where I live.
--Just like at home, be conscious of portion sizes. If you are at a buffet, take a salad or dessert plate instead of a platter. If you are in the dining room and it isn't really yummy or you are full, leave the rest on the plate. Before you go back for seconds, ask yourself if you are really still hungry.
--What makes a salad good to me is fruit, meat, croutons, and a yummy dressing. So I usually don't eat them at home because they end up being 600-700 calories! Similarly, I only ate salad on the ship twice (because I knew I needed more veggies that day), and when I did I chose the low-fat dressing. Eating 200 or 300 calories worth of dressing is NEVER worth it to me.
--I don't drink alcohol, so those calories weren't a concern for me. If you enjoy that, be sure to be aware of how much you are drinking because those calories aren't free!
--Basically, decide that if you are going to put on several pounds, make sure every bite is worth it!

In other words, just like at home, stay active and hydrated, make reasonably good choices regarding food (not depriving yourself of things that are special or really good, but also not feeling like you have to get your "money's worth" by stuffing yourself). I had also planned on weighing myself every morning in the fitness center so I'd see the weight coming on as I went, but that didn't work because it was a spring-style scale and as the ship swayed, my weight would fluctuate within a 10 pound range!

I did gain two pounds on my home scale, but after 11 days of being at home and eating at a 250-500 calorie deficit, it's off again so obviously it was some water/waste weight and not 2 full pounds of fat, since my deficit wasn't 7000 calories in the last 11 days. So effectively I took a short break from my weight loss and maintained for 3.5 weeks while enjoying a cruise. I can live with that.

If I were to go on a cruise, I'd make exercise my number one priority to start the day so that I can then enjoy the food I eat throughout the day.

Two hours in the ship gym first thing in the morning would be my plan. I'd look for a nice 1000 calorie burn every day - which can easily be achieved with a fast hour on the treadmill, 30 minutes on an elliptical and 30 minutes on a bike.

Do that from 6:30a-8:30a, take a shower, and then have a good breakfast at 9 a.m. every day. Then continue throughout my day doing what others have said - lots of steps, stairs and moving about as part of the day. But that would be IN ADDITION to my 2-hour daily gym exercise.