Not sure why the ships would do that though as I do not think they allow alcohol to be brought on board now. You either buy it on the ship at their prices or you buy their drinks.
All the major cruise lines permit you to bring alcohol purchases on board in a port of call such as St Martin - but the ships require that you hand it in for storage on board until last night of cruise when it is returned to you.
(There are some rare exceptions when ship lets you take it back to cabin - usually because ship does not want to have to store and then return all of it. This happened when we were on Empress visiting Havana - the amount of rum bought was huge and Captain - at least on our cruise - let people just take it to their cabin.)
