Whether you like to drink coffee or iced tea or water or lemonade on the cruise ship, I would recommend getting an insulated tumbler to bring with you.
The coffee cups are coffee cup size on cruise ships, so if you like to have more caffeine than that to start your day a stainless steel mug comes in really handy. In addition to being able to fit a whole lot more, you can get one with a top, so it’s easier walking around with it.
Also, if you prefer to have iced tea, lemonade, or water, then the same sort of thermal mug comes in handy, rather than going with the plastic cups they have on board.
Some bartenders may even pour soda or other drinks directly into your personal mug, too, or else you could always order the drinks and pour them in yourself.
You can get a really nice one from YETI, but there are also lots of other brands for less that get the job done.