You’ll probably take U.S. 71. In Carthage, Whistler’s Hamburgers is a daytime place on old 71 a few blocks north of downtown.
Joplin is a few miles west of 71. Stop at Fred & Red’s, a chili place that’s been in its current spot since the 1940s and looks the part. A local institution that ships chili all over the country. At about 17th & Main. Open Tuesday-Saturday. Never in August, though.
In Arkansas, check out AQ Chicken in Springdale and Fayetteville (http://www.aqchicken.com/). I love the oven-fried chicken.