True a passport is a very good ID, acceptable universally.
Too much time at Carlos & Charlies or Senior Frogs Over ? LOL, I've read about people like you.
Ha!....well, ya actually......
but it's the non-cruiseline endorsed tours that could get you in trouble. The ship will wait for any of its own tours/outings that are late getting back. But if you book one yourself, and it's held up for some reason, the ship leaves without you!
That's when you need your passport to fly outta there (and hopefully meet the ship at the next port!)
We were in Jamaica once, and the ship waited over an hour for a late returning excursion.
And going out of New Orleans one time, the ship waited a couple hours because a plane was late.
Neither of these caused us to be late getting to the next port. I guess they can make up time cruising faster thru the night.