Ignore the % off/BOGO type sales on things like drink packages, just look at the bottom line price.  There is no rhyme/reason it seems to how they advertise some of these things.  If you're happy with the price, book it.  You can always cancel and re-book if the price drops up until 3 days prior to sailing.  Note that when you do this, OBC used is refunded immediately but money to your CC can take a few days.