I would be a little concerned about unpainted OSB in a unconditioned garage as it may absorb some moisture in the right climate and swell over time.
kachi's masonite (holeless pegboard) option may work for some people. (can't believe I'm agreeing with him on anything
). It will take paint well and is very cheap. But it won't hold any weight. You need to find a stud to hang something heavy from it.