I would suggest sleeping in that day, then spending some time in the pool or at the resort. Sometimes you can get your check out extended for an hour or two. Check your bags with the bellmen and head off to a park or to resort hop. You will need to be at your resort at 6:00pm to get your bags and be picked up by the car service driver.
Plan a nice sit down dinner for about 4:00pm. We also almost always spend our last day at Epcot, not sure why, but it seems to be a good last day park.
If the weather is really nice, just keep a plastic laundry bag and change of clothes in your carryon, and head for the pool. Swim in the afternoon (you're allowed to use your resorts pool the day you check out up until midnight), get changed, and have an early dinner (you'll need to eat before going to the airport, if it's really busy you might not have time there, and they probably won't serve a meal on a flight that late.)
Anne