I can attest to that, on our first Princess Cruise, back in about 2006, while docked in Barbados, I walked into a port duty free liquor store to see Mount Gay Rum ( locally made in Barbados), being sold for about $7 US for a 1 litre bottle ( approx. 33 ounces). Obviously I could not purchase any to enjoy back on the ship, but while walking towards the Sun Princess, what do I see? The ship is being loaded with supplies and amongst these supplies I see literally pallets of Mount Gay rum being loaded on to the Sun Princess! I do believe at the time a drink on the ship was about $5 US. Not taking into account the labor cost or cost of mix, which are both minimal, that one bottle of rum is paid back in probably two drinks, even at a generous 1.5 ounces per drink, the remaining 30 ounces of that 33 ounce bottle is pure profit. Nice margins. Reminds me of popcorn at a movie theatre.