I went on a cruise in Sept (princess) and found it very easy to stay Low Carb. Bacon and omelet for breakfast, salad bar with choice of deli meats and/or fish at lunch and meat + veggies at dinner. We quickly learned we could order extra veggies at dinner, gratis. For exercise we walked around the deck multiple times taking in the sights.

This would be a good opportunity to try new veggies - start with one bite - to see if you can expand your food choices.

Our cruise line would not allow us to bring water or more than 1 bottle of alcohol on board, but I was able to buy a coffe/drink card which discounted the water significantly.