I wouldn't give him milk. Cow milk actually can do more harm than good. Baby bunnies have very sensitive stomachs. Goat milk works the best. Also, if you've never fed a wild bunnie before you can do him a lot of harm, because you don't know the proper way. For the little while untl he wildlife center opens I would just keep him warm (put a heating pad on low under the box, feel it to be sure it doesn't get too hot.) I wouldn't give him milk if I were you.