Do you just mean on property? We enjoy touring the different resorts. Maybe plan a meal at one of them, or just do their counter service option, but take some time walking around.
Buy Steve Barrett's Hidden Mickey book and use it to search each location for the hidden Mickey's. We've gotten hours of fun out of that over several trips.
Do a "progressive dinner" along the monorail route or around the path connecting Boardwalk and Yacht and Beach club.
Go to the ESPN zone if you're a sports fan and watch a game while getting some food and drink.
If you don't own DVC, sign up for a tour. Even if you have no intention of buying, it is fun to do and they usually give you some perk for coming. We got gift cards and free ice cream when we did it a couple of years ago.