I'd say sleep in a little bit, relax in the morning, maybe some tv time, or grab a bite, head down to the pool before lunch.
-Boardwalk doesn't have much going on during the day, as pp's said, it's pretty and you can look in a few of the shops but thats about it
-Play some mini golf
-Head on the bus to Magic Kingdom and take the monorail tour, explore around the Contemporary, Poly, Grand & maybe even take a boat to Wildnerness lodge to see it!
-Make a dinner reservation in this area to have a nice meal OR
-Take the boat over to Fort Wilderness to do Hoop Dee Doo, which is my favorite thing on property, OR, check out Mickey's Backyard BBQ. Depending on your timing of Hoop (if you do the 6:30 one) you could head over to the Chip & Dale campfire sing along/movie & roast some marshmallows.