If you make it liquor inclusive, it should be all inclusive...including excursions, spa, laundry and caviar with a credit of a certain amount to be spent individually. It would be great to have NO bill at the end. Some passengers drink, some spa, some caviar, some like to get off the ship and do things. By offering only one of these options, you would not satisfy all.

You'd still have to sign, but it would be offset to a credit.