I have worked on Royal and of what I know you could buy achohol out side but if they see it they would most likely tag it and help you hold it untill you leave the ship. That is because that's the RCCL's agreement to the duty free shops (not owned by RCCL) since they sell achohol on the ship. But if you buy the bottle from the shops there I would imagine you could drink it in your cabin.

Even if you buy alcohol on board,tghey hold it for you until you disembark.Maybe you can sneak tiny airplane bottles on.
I just returned 12/16-12/19/2005 I am just wondering if the alcohol was watered dow.,because I should have been really wasted.I watched them pour the rum,and told them to put more,