Years ago before 9/11, I preferred booking my airfare. It was great to drop off your bags when you walked into the airport and not see them again until they arrived in your cabin on the ship.
Now everyone has to go and claim your own baggage and that's where the shuttles leave from.
There are several options on how to get to the pier.
We are cruising out of Honolulu in January and I've found numerous forms of transportation ranging from a shuttle at $12.50 to a limo.
I to always go a day early. It's worth the extra money to stay in a hotel and not sit worring all day if you'll make the ship. Ship's usually sail when it is time to sail...unless there is a large tour group that is late.
Have a great time!