On RCCL you cannot even buy liquor in Port and bring it on board without it being taken and stored until you leave the ship.
We were on deck watching passengers board in P.V. Mexico when a group tried to bring a couple of bottles of Tequila on board. We saw Security attempt to take the bottles but these passengers decided to open and finish both bottles right then and there. WHY???? We think it would have been a lot easier on them just to give the Tequila to Security and it back when the cruise was finished. But it did make for some good entertainment watching them try.