My husband and I have been on a low-carb (not true keto) for over 4 years now. At our peak, his weight loss was 135lbs and mine was 55lbs. We've allowed occasional cheat meals in the last year, and been less physically active, so I'm up 5lbs (sitting at 135lbs as of this morning). Overall we're really happy with the low-carb way to get our weight down, but now we're mostly focusing on maintaining.
I will say that if you stick to low-carb for many months, you'll see consistent results which is super encouraging. We fast from 8pm to 1pm the next day, and have a lunch of cucumber, a pepperoni stick, a piece of cheese and a hard boiled egg. Dinner is a large serving of veggies (usually zucchini, peppers, broccoli, cauliflower or a salad) and meat. Having done this for so long, I've created all sorts of recipes that really work for us, and the selection of low-carb speciality items has increased so much (like keto bread, hot dog buns, tortilla wraps, etc).
Having said all that, when you're deep into keto, your body doesn't retain water the same way it used to. A lot of your initial weight loss is just bloat. So if you plan to eat everything on your cruise, I would say to expect your weight to increase at least 10lbs in a week--and MOST of that will be bloat!
From my experience, if I have a carb-binge but avoid sugar, my recovery is pretty quick and any weight gain is minimal. However, carb-binges that include sugar (such as donuts) are MUCH harder to recover from and the weight stubbornly holds on much longer.