If I have room, I pack rum, vodka, cordials, etc. either in little nips or small plastic Water bottles. I just like the convenience of making my own drink in my cabin. Also, bring a sports water bottle and you can make your special drink to sip by the pool. They will not allow you to bring on bottles of liquor in open packaging; bags, boxes, etc. They will keep them until you disembark. I had a bottle of sparkling water and they just asked what was in the bag. Water or soda is OK to bring on board.
Bon Voyage