beachy1nut:

Carnival doesnt  encourage guests to bring alcohol.  Officially the  policy is each adult over 21 may bring one bottle of wine onboard. 

People do "smuggle on" alcohol.  You can purchase 'virgin' drinks and spike them with your smuggled booze.  But  as you arent supposed to have it with you,  you arent really purchasing a set up.

According to Cruise Critic the setups you buy from Carnival do include the liquor. They think buying the bottle from the ship is a better deal than buying multiple drinks. This a post from the setup thread:

"I did the in room set-up (bar that is) on the Gem 5/31/09 and it was $63 for a 1 litre bottle of Beefeater Gin. I am sure someone will help you and post the email address for ordering the set-up. And then you don't have to visit the "Naughty Room".

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Regina girl you have a mouth like me lol!!!! This will be me and my husbands first cruise. It is our honeymoon we got married June 27th. Im so excited but am nervous at the same time. Can you give any advice our info that we as new cruisers should know. We are leaving July 16th on the fantasy 4 day!

so you can bring a box of wine and have it count as a bottle or is there a 'size' limit?  wondering how a box/plastic inside would fare on a plane though - would be a disaster if it exploded in my luggage