Last year on the Ruby out of GLS, Princess drink package kicked in as soon as we hit international waters, if you sail at 3, your package will start about 1 1/2 - 2 hours later.
Prior to that due to TABC laws you are required to purchase Texas alcoholic beverages (those paying Texas tax). You are also charged for those. Most people use their OBC for those purchases, however we bring a couple of bottles of wine which suits us fine.