Seriously, apples work very well. It really depends what time of the year you want to feed them. Corn and similar grains work great during the winter months when food supplies are reduced. In box traps. the apples used to be the bait of choice.
If you have never hunted rabbits with dogs, it is a real blast. You can get hooked really easy. In my youth, some of my most memorable hunts were for rabbits using two dogs after school. Started with a shotgun and that got too easy as I loved the chase more than the actual kill. Gravitated to using a 22 auto rifle and then moved to a double action 22 revolver (actually both). Great Fun!