This is exactly what I do. Yes, I'm on WW but that is a program for living, not dieting. I will do stairs as much as possible and use the walking track, and I'll be aware of what I'm eating and do some things like ask that my servers not bother with heating up gluten-free bread for me at dinner (easy since I'm usually solo...or with my parents who are gluten-eating, so they can have their bread and I'm not tempted), but I don't deny myself.
One week (or 8 days in the case of my last and next cruises) is not going to make or break me. I know how to get back on track.