Ii've done all of those things in the last two legs of the journey
Just an observation, but roadtrip can be much more than checking things off a list. Sometimes revisiting places you've already been, especially when they are already on your way, can really provide a new perspective to a place and let you see things you may have missed in previous trips.

Having said that, there are many more things in the Black Hills, like Jewel and Wind Caves, and Custer State Park, just to name a few, that you could also explore on your last days.