Another vote for the day before. We actually got in late on Thursday night for the Saturday sailing. Rented a car at Budget at the airport, and had no problem finding Ron Jon's in Cocco Beach at 11pm. I was very nervous about this part of the trip, as we haven't been in the area before and we were on a late flight. It went great. The rental was super for the next day-drove all areound the area in the morning and had planned to go to the Space Center, but decided to head back and enjoy the pool area at Ron Jons, (which closes at 5pm by the way, so plan accordingly. In my opinion, there's no need to stay at Ron Jons if you can't take advantage of the pool area, although it's the closest to the Disney terminal.) The morning of the cruise we had a nice breakfast, dropped the rental, and the four of us and our luggage had no wait going over to the port for 10:30am. However, we were able to check in the express lines because of our cabin, so if ressies are a top proirity, I would plan on getting there as early as they start allowing you in to get a place in line to board.
On the way home, we decided even though it worked out to be a bit more money, to take the Disney bus from the port to the airport. I arranged this transfer while we were on the cruise by visiting guest services. I picked a slow Wed. morning and had the whole thing done in 5 minutes. The debarkation day we found our luggage, and the Disney staff is outside the terminal helping you find the proper bus depending on your desintation:
WDW resorts; & the airport according to airlines. All very easy to follow. Just make sure you see your bags go on the same bus that you are getting on....
If you decide to do a one way rental from Cocco Beach, you go across the street from the terminal to the white canopy area, and the rental companies have shuttles to their establishments.
Hope this information helps!
Kathy