Agree with the obedience suggestions. Now is a great time to proof down stays! Read up on shaping, if you aren't familiar with the term. When my dog was on crate rest, we shaped a lot of safe behaviors--"go to your mat", nose touches, pulling tissues out of a box, going around an object, etc.
Also think about games like hide and seek. Hide individual kibbles around the house instead of using a bowl at meal times, and let him sniff them out.