nothing more exotic than defrosted mice. I've kept WC Western coachwhips several times, and am currently holding three in quarantine prior to adding them to my collection--they all eat defrosted mice, and have since the first attempt.
Coachwhips are opportunistic feeders in the wild, and take carrion pretty regularly, so a d/f mouse is pretty much the same. I offer a bark hide, which the snakes stay under when someone is in the room (they come out if I sit still and wait a bit), and lay the mouse at the end of the bark, maybe just under the edge. In a short time, the snake usually sniffs it out and I see it getting dragged under the bark.
Hatchlings are a different story. They may need scented food, or actual prey like lizards, fish or frogs/toads. They are too adorable, though, and worth the effort.