The Jazz Museum and Negro Leagues Baseball Museum are connected, so you can do both in the same trip. Those aren't too far from the convention.

Worlds of Fun is adjacent to Oceans of Fun, which is a water amusement park. It might be warm enough for you to go to the water park. It's going to be sunny with highs of 80 degrees or higher. That's a bit outside of the city, and further away from the convention.

Either way, trust me, there's stuff to do. :D