It really would be a state-to-state issue, but the general rule of law is that if someone has left property in your care, you can be reimbursed for the costs of protecting and caring for the items. For example, a portion of the insurance that covers your garage could be considered an expense of caring for the items. Is your garage heated? A portion of the heating bill could be an expense... One thing I would suggest is that you photograph what is there, it will help if you have to establish what was left.
Additionally, if you know where he is, I would send him a letter (certified mail) to tell him if he doesnt make arrangements to get his things within ___ days, you will dispose of them.
Lastly, I'd make a quick call to a local lawyer and ask him how long it would take for property in Ohio to be considered abandoned. Once that period has run, you could likely do whatever you wish with the things.