If you are fitting a day off inbetween going to the parks, I'm sure the favorite activity of the day will be to sleep in!!! LOL.
Yes, we find lots to do at Ft. Wilderness on our non-park days ... rent boats on Bay Lake (from Marina - watermice, pontoons) ... from bike barn at Meadowlands Recreation center you can rent fishing equipment, pedalboats, canoes, bikes, golf carts. At the Meadowlands Recreation area you will also find a shuffleboard court, tennis courts and volleyball courts. Teatherball can be found at the end of the 1500 loop. And there is a swimming pool and arcade.
At night there is a sing-along and a disney movie. You can buy marshmellows to roast over the fire.
You can watch the water parade from the Marina beach.
There is a petting zoo at Pioneer hall. There are trails to walk/bike.
So many things.
Ride the ferry to the various resorts and explore.
Visit the gift shop.
Have a pizza/beverage at Crockett's Tavern. Enjoy a buffet at Trails End.
There is horseback riding, carriage rides, etc.
You name it .......Lot's to do.