It all depends....on ourlast trip, on the day we went to MGM, RnR was down for most of the day, so on our last park day, most of the group wanted to head over there. Another time, Space Mountain was down, so we made time to go back to MK, though not on our last day.
Usually we leave our last park day very open, so that we can go back to whatever we missed, or the rides that eveyone wants to hit one more time.
I should say that we usually fly, so for us, the idea of getting out of the park, to the car, and to the airport in time makes me a little uneasy. So our last half day, we most often do non-park stuff. Sometimes we use the last day to go to DTD. That way we can buy souvies to bring home at the WoD store, esp. if you want to get something for people back home. Another thing we've done that last day, was to have a nice breakfast or lunch at a resort, and/or maybe go swimming. Most of the resorts have a changing room right next toth e pool, so you can do this without having to go back to the room. We also have a curious fascination with eating at a Waffle House...driving to the airport and back is sometimes one of the few times we're off property, so that's been one of our stops too. If there are any other offproperty places you like to eat, that last day can be a good time to do so.
