I was just on the Carnival Freedom over Xmas , first timer so I also did not know what to expect . I had read some forums online and asked friends who had done a few cruise this same question. I was told pour your clear drink of choice into water bottles , put your alcohol in 1 litre pop bottles etc. Well I wrapped up a bottle of rum in a towel in one checked suitcase and a bottle of vodka in another suitcase. Both made it just fine to my cabin . At our first port of Cozumel bought a bottle of tequila as a gift for a buddy ,brought it back to the ship in a plastic bag .I placed it in the ships xray machine expecting it to be taken from and held till the end of the cruise . Well it was not , picked it up on the other side and took it back to my cabin . In Jamaica bought a bottle of banana rum

and again placed it in the ships xray machine upon returning to the ship . Again picked it up on the other side and took it back to my cabin . Not sure if this is the norm but never had any problem with bringing my own alcohol aboard the ship