I take a glass of unsweet iced tea to the bar and have them add a shot of Grey Goose. Then I add a packet of freeze dried lemon powder and a packet of stevia powder (both available on Amazon). With white wine, I ask for a glass of club soda and make a spritz. Reds I choose dry-er varietals. I also take 3x Milk Thistle per day, which helps kick the alcohol out of your liver. I also used one of those tiny Ziploc cups and had a scoop of Perfect Keto flavored collagen in it for after dinner coffee, or morning coffee. X ships now have Truvia packets all over the place, but sometimes erythritol upsets me. Was good in a pinch though if I forgot to pack stevia.
I stay away from any drinks made with soda "Zero". They use Sucralose as the sweetener. Sucralose always spikes my insulin and triggers my hunger hormone so I tend to crave salty snacks and ice cream. I use Zevia soda as a mixer at home, so I know for certain it's the Sucralose that does this.
We just spent 3.5 weeks in Europe on two ships - RCCL and then X for the crossing, and my net gain was 3 pounds. Not terrible, considering I had croissants delivered via room service every morning, ate at Eden twice, and had dessert every night. Didn't take me long to get back into keto once we got home, and I actually think the break helped break the plateau I had been complaining about for some time.
Oh, and even though it was a heck of a lot easier the first half of the cruises than later when I felt fat and bloated, we took the stairs everywhere. Up and down. Only took the elevator twice - once on the way in with luggage, and when we got off. I averaged 10k steps every day - even sea days.
Good luck!