I'm guessing this trip includes everyone in your signature yes?
My usual non-park day would include:
-Sleeping in! (make sure to put that do not disturb sign on the door)
-If you feel like swimming, do that for a bit,
-Relax, watch some TV
-Head to DTD for some shopping, maybe even a movie? I know it can sound weird, but it's a way to put your feet up but still be in Disney, and I really love the dine in theater!
-Monorail resort tour! Take the bus to mk, hop on the monorail & explore. You can grab a snack or bite at each hotel to share/sample it all, adults could grab a drink depending on time.
-If you're more adventurous, explore DAK Lodge, look at the animals, grab some African inspired food there!
-Wander the Boardwalk area/resorts, relax on the Yacht Club beach, grab some to go ice cream from Beaches & Cream, some pizza from the window on the BW
-Fort Wilderness has A TON of things to do for a little bit of money, you can trail ride, wagon ride, explore the stables, rent a boat (this can also be done from other lakeside resorts), Mickey's Backyard BBQ or Hoop
-Hoop Dee Doo or Spirit of Aloha is a great option for the late afternoon/evening as well!