If it's one of those all you can eat free buffet style cruises, you'll need to think more about how insulin generally lasts for about 4 to 5 hours. So, if you have lunch and bolus x for it, and then a few hours later decide on a mid-afternoon snack, you'll be calculating y units for it, but remember you'll still have active insulin on board from the lunch shot, and it'll be peaking after about 1.5 to 2 hours, so you might want to be thinking about maybe reducing the snack bolus a bit, otherwise the combined 2 boluses working together can be unpredictable.
Some meters have an insulin on board feature to get a rough idea of how much is still kicking around. Libre has too - code to get intonthe professional options to set it up is CAA1C.
Maybe just experiment a bit by getting a sun lounger near the cake trolley in case of emergencies!