A couple of ideas depending on your interests.
Must see: Truman Presidential Library in Independence and his home located in the same city.
Other suggestions , Ft. Leavenworth and the city of Leavenworth. You may do some research on getting onto Ft. LV with an RV. It is a restricted access post since 9/11. The museum is great and the self guided tour is nice. Lots of history.
The Nelson Atkins Art Gallery in KC.
Atchison KS has a nice Amelia Earhart museum and the college has some interesting architecture.
Weston MO has the McCormick Distillery and a small town atmosphere.
Sad to say the only place you can get a Runza down here is in Lawrence KS. The one on Johnson Dr in KC just closed.