Depending on where you are actually going, some Caribbean and the US Virgin Islands allow more but the norm is one liter duty free, over that.
Duty is generally 3% of value and the IRS excise tax is generally between 21-31cents per 750ml bottle of wine, 67 cents/champagne, and $2.14/ hard liquor.
Then to ponder deeply, if you are flying to and from the port, how are you going to get it home, no matter what the quantity. You are no longer allowed to carry it on so that leaves checked luggage. Down side of checked luggage is: Breakage due to the gentle handling by airport baggage handlers or just plain baggage handlers with a lust for rum cream. On the other hand if you are driving to and from port, go for the gold. Adding 3% and $2.14 to duty free booze will still beat anything you can find at Walmart.................