Whole grain Cherrios
Just break each one up into a couple pieces, and watch him when he chews it, make sure he is chewing and not hoovering it. If he hoovers things, be careful about what you give him.
I would just put the treat in the crate, leave the door open and let him go to it. Then treat him for going in
Have you heard of clicker training? I have had the best success with this method
www.clickertraining.com