What if you have applied for a passport but it won't arrive by your departure date?

The passport is an absolute must for any cruise traveling to a port outside of the home port's nationality. You won't get onboard without it. In the US, you can get your passport expidited for an extra $60. There are also three cities in the US you can get your passport on the same day you order it. One city is Miami. Check out the US passport website for details at travel.state.gov and look up "How do I get my passport in a hurry?"