What are some things I must do on a road trip around the country?

Me and my 3 friends are going on a road trip around the circumference of the United States. We are originating from Pittsburgh, PA going through Michigan to Minneapolis then on to Grand Tetons, Yellowstone, Glacier National Park, Seattle, San Francisco, LA, San Diego, Las Vegas, Grand Canyon, Austin TX, New Orleans, Atlanta, Charleston, and then back to Pittsburgh. I am looking for fun and unique places to stop or do along the way. Thank you in advance for all your answers and I will be giving ten points to the best answer.