You can get a couple of bottles worth of Bacardi 151 on a cruise ship by pouring it into a large empty bottle of original carmal color Listerine.
For my only cruise, I took a 24 pack of bottled water. I carefully emptied the case without disturbing the plastic wrap around the case. I then emptied the center bottles and filled with vodka. I then glued the tops shut (in case someone tried to open one). I then reassembled the case. I got two liters of vodka on board with no one the wiser. We only drank before leaving the room and after entering the room. We still bought mixed drinks, so it was not obvious what we did. Oh yeah, we tipped the room staff pretty well.