We booked a last minute Carnival Cruise and will be departing in October. We don't have a passport for our 16 month old. Since we will be driving to Galveston, I know that we don't "need" a passport, but I've heard that it can speed up debarkation (as well as be useful in an emergency). How true is this? Should I pay the fee the expedite the passport, or just go with a certified copy of his birth certificate? Thanks!