Many cruise lines FORBID that. They make a great deal of their profit by selling the Drinks packages, and expect all drinks to be BOUGHT, on Board. There is also the waste disposal issue of all your cans and bottles, which they do NOT want. ....as THEIRS have to be carefully handled and managed.
There is also now the same concern about TERRORISM and liquids, that Airlines have. They do NOT want you bringing ANY unsecured liquids on boards, that THEY have not inspected and okay'ed first.
They also do NOT want you trying to avoid paying for the DRINKS packages......as it cuts into their profits.
On Costa......you cannot even bring a bottle of open Coke back on board with you. Just like Airlines, they will take it from you at the security checkpoint.- No exceptions.
On my last cruise........we found a store selling Mountain Dew, in Ibiza, and we bought them out, as they don't sell it here in Italy.......but when I got back to the ship, they gave me a hard time.
I had to explain that we already HAD a very expensive drinks package......and this ***WASN'T**** for consumption ON the ship, and that our intention was to simply bring it back home with us, since it's not sold in Italy.
They were not happy at all......but decided to let us pass.....and I had to give my SOLEMN word, that we would NOT open any of the bottles or cans on board. I even offered to let them HOLD it for me, if they wanted.............and that put them at ease.........so they allowed it.