They do have a departures lounge at Aulani, so you can store your luggage, do other things around the resort, shower, etc. That's probably what I would do.
I always hate to load everything up in the car and go around and do things, because I'm worried that people will break in and steal stuff. We had our rental car broken into once on the Big Island when we were eating at Bubba Gump's. They took two portable DVD players, our electronics bag, and a big package of diapers we had just bought.
We usually try to schedule things so that we leave to fly home the evening before our check-out date (when we can't fly in the morning -- which I don't think you can do in Hawaii). That way, we have use of our timeshare right up until it's time to fly home.