I too was going to suggest Rays of Kelso. One other place you might try was just a bit east of Cape about 6 miles in Gordonville is the Gordonville Grill:
829 State Highway Z
Gordonville, MO 63701
Another small piece of American is in New Hamburg, MO alsoa very short drive from Cape. Schindlers Tavern serves fried bolgna burgers which are awesome. I'm a big boy and I could barely handle the double cheese topped w/ 2 slices of fried bolgna. Might tasty.
Right across the river in East Cape on the south side of the road is a driveup called Babes Fish House. Very good and quick fried fish. I highly recommend the buffalo ribs. Like a big toothpick w/ very white fish on it. They have sporadic hours and the owner just passed but it is wortha look see for sure.
Last year I went down to Cape for two concerts and prior to both concerts we ate at Broussards downtown. Not too impressive to look at and the service was not great but the food was good. Each time we had servers who were new. It has cajun and american food. We had crab legs. steaks and jambalaya and enjoyed them all.