Yes, on board Atlantica has a lot of shop and a big duty free with cigarettes, alcholics and others...I don't know if in Caribbean there is a different law about duty free shops but in this Summer season on board you colud buy them but about alcholics' bottle Costa delivered them only the last day of the cruise.
Lots of shops... actually a very nice shopping "street"... Via della Spiglia... or something similar. Think Teo is right... liquor purchased on board is delivered to your cabin the day before you return. Ernie