I'm getting ready to go on a cruise in March & have researched this subject extensively.
The basic answer is that officially, no, with most lines you can't bring your booze on board (anymore - this is a newish policy). However, some lines allow you to buy from the shop on board (the retail shop, not the duty free) and take to your cabin for consumption there. It is considered extremely bad form to drink your own hooch in public areas of the ship, though nobody would know if you took your glass from the bar area and refilled it in your cabin.
The worst that can happen if you bring your own is they'll take it when you embark and return it the last night of the cruise. But I have heard many stories of winks/nods and people getting on with their own stuff. You can bring your own sodas on - some people fill entire 1 or 2-liter sprite bottles with their own vodka. A ginger ale bottle would work for rum or whiskey. If you are careful taking the cap off so as not to bust off the little 'ring', you can put the cap back on and the bottle looks unopened. 20 oz plastic soda bottles would work this way too. You could probably get a rare scotch/tequila on undistguised without much trouble - particularly if it isn't something the ship carries.
One lady told how they wanted to take her stuff when she got on the ship. She took the [whoever it was - the purser I think] aside and politely informed him that in that case, her bar tab would be subtracted from his tip. Her hooch was let aboard.
It really boils down to the officers on the ship - they have nothing personal to gain from the 'no booze' policy - but they are stuck enforcing it. Some will be nice, others won't - your mileage will vary. In any case, if you do get your stuff on and into your cabin, be discreet. And leave a decent tip on the first night in your cabin for the cabin steward. (S)he is the person most likely to notice you've got your own - so $10-20 on that first night will ensure a trouble-free time. FYI you generally tip at the end of the cruise - in this case you give a little cash at the beginning. Don't subtract it from your tip at the end.
For more info on this subject, go to google.com. Click on the 'groups' tab at the top so you are searching newsgroups not the web. Then enter searches like 'cruise liquor sneak' and see what you get - there's a ton out there - maybe even on this ship/crew.
If you are taking your suitcase on an airplane, make sure everything is in plastic bottles and well padded!
Guests are prohibited from bringing alcoholic beverages on board the ship in the port of embarkation (with the exception of wine and/or champagne). If the wine and/or champagne are brought to the Dining Room for consumption, a $10.00 corkage fee will be charged to the guest. Otherwise, the guests may drink the wine/champagne in the privacy of their cabin ONLY. It may NOT be brought into any public lounge or room.
Alcoholic beverages purchased in any port-of-call will be appropriated at the gangway and stored onboard until the last night of the cruise, upon which it will be delivered to the guests's cabin.
Alcoholic beverages of any kind purchased in the ship's gift shop will also be stored onboard and delivered to the guest's cabin the night before debarkation.
The minimum age for the purchase and/or consumption of alcoholic beverages while on board is 21 years of age. In the event that Bar/Restaurant/Gift Shop staff are in question that the guest is under 21, they shall request picture ID prior to serving such guest.
The legal drinking age of 21 is strictly enforced. Adults are NOT allowed to purchase drinks or bottles of alcohol for minors. Possesion of alcohol by a minor will not be tolerated and any found will be confiscated, even if found in cabin.
Thanks for your inquiries and comments. (hiccup)
Bahama Mama