I suggest stopping to eat at Kroll's Kitchen or Scotty's Drive In. Kroll's Kitchen in Mandan is 50s style dining with good food. Scotty's Drive In in Bismarck has that old time feel with a car gathering and the food is decent.
If you decide to go and want any tips on hotels, etc let me know. I know the area quite well. Many of the hotels fill up fast and many nice classics in the parking lots or running around town.
"An ignorant man thinks he knows everything, a wise man knows he doesn't."