All bags that go aboard get scanned so think about transefering the contraband to something that doesnt look like a bottle of contraband.
Also make sure they wont break or leak.
If your going on NCL they are pretty aggressive at snagging stuff. Other cruise lines tend to look the other way unless its spring break type travel time.
A quick seach here will yield numerous threads discussing this and various ways people go about it.
CCL Inspiration 09
RCCL Explorer of the Seas Eastern 09
CCL Miracle Southern '08
RCCL Enchantment of the Seas Western '07
PCL Caribbean Princess Eastern '05
RCCL Explorer of the Seas Western '05
RCCL Explorer of the Seas Eastern '04
CCL Destiny Southern '01
CCL Sensation Eastern '94
CCL Ecstacy Western '92
CCL Jubilee Eastern '90