You may be able to leave your luggage at the airport, though it may be costly. Hotels will hold your luggage, but if you are not staying at one, I'm not sure if that would work either.
Some people prefer to board as soon as their ticket allows. I personally like waiting for several hours, so I can tour the city, and have no lines to wait in.
Have a wonderful cruise.
MamaofEnS
NCL Sun March 2008 Carnival Destiny June 2006 Carnival Ecstasy June 2002 Carnival Elation August 2000 Celebrity Century June 1998 Carnival Carnivale August 1993