dnitz1:is it illegal to bring black coral back to the states
Better not be.
dnitz1:where is the best deal to buy alcohol. on the ship or in port.
At your local package store, frankly.
Unless it's an imbibable you simply cannot find here in the US [like Xtabentun], what's going to happen is that you'll run up to your Customs limit in short order [and you are following import rules...]. Those you buy in excess of the allowance are assessed a "duty" that more-less equals the difference in what you'd pay abroad versus the package store down the street.
And then you still have to cart it around and put up with FAA rules and their inspections and the risk of it breaking...
Four bottles of Jamaican rum from your local package store are [say] $10 each, including tax. $40 total and you have to carry the bag from the store to the car, and then from the car into your house.
Four bottles of the same Jamaican rum from Jamaica are [say] $8.50 each, and you have to cart them around Jamaica until you get back to the boat where they take them from you. $34 so far. The last night they give them back, and you fill out your customs form, claiming the two extra bottles [you're allowed two "free"]. The Customs weenie will charge you [say] $1.75 per bottle for the two extra -- another $3.50, for a total of $37.50 on $40 of rum. Then you carry them for an hour while you're getting off the boat. And even if you were smart and packed them in your checked luggage so you don't need to feverishly repack at the airport, United is still going to tell you that you've exceeded the weight limit on your checked luggage and add another $20 to your check-in fee.
If you're driving away from port? that's the only time it might be worth the effort of lugging them around.
If you can find it at home, you might just as well buy it there.
Desperately seeking 10th cruise for the free laundry.