Driving i-35 between KC and Des Moines
Honestly, I've made that trip hundreds of times, and really can't think of anything that was worthy of mentioning. Just north of Bethany there is a Mexican restaurant that was pretty good, but not that noteworthy. You might get luckier if you stray farther off of 35, though.
Secret Spots from Trza:
Sale Barn Cafe: in Lamoni Short hour cafe closes at 2pm, homemade everything from pies to casserole to baked bread and full breakfast. Outside smells like cows. Call ahead.
900 E Main St, Lamoni, IA
The Dinky Diner in Decatur City serves a good breakfast in an original double-wide prefab diner manufactured in the fifties.
The Roadside Inn in Martensdale advertises a "famous giant loin" on the menu, but you can find a better one ten miles off the freeway in Old Peru, right next to East Peru at the Peru Bar and Grill, get off on the Truro exit. My review is here:
325 N Highway 28, Martensdale, IA 50160
104 NE 4th St, Decatur, IA 50067