I have never been on one but I have family that have gone. They did one of those island cruises where you stop off at a few places, one being Jamaica. Always wanted to go there but honestly, me and boats don't mix (I don't know how to swim lol).
As far as I know, they have specific zones for smokers on balconies away from people. Not all of them have these though so you have to look into it. Sneaking alcohol, not sure. Better off just buying it on the cruise. It is overpriced but from what I heard they have some killer drinks you can enjoy. Just drink moderately so your wallet don't suffer.