I don't believe there is any gratuity on the mug itself (only the beer), but I've had mine for a few years so I could be wrong. I would wait until you are on the ship since they have tons of them and you can just request one when you get your first beer. They also have people selling them right after you get onboard, along with water, beer packs for your room and some other stuff. This way if you change your mind you aren't locked into the mug. Also, like someone said above, you can get it right away, not when your room is ready. If you buy it outside of a bar, I recommend having them swap it in the bar for a clean one, though.