Couple points to consider.
1) if the hole and hanger are for light weight
materials like a cargo net to hold a clothing bag, then find the largest diameter screw that doesn't pierce through the plywood. Maybe a 3/4 in long #10 or #12 hex head or Phillips button head wood screw.
2) if you want to hold down a generator
or ice chest, then make sure you are using something like a 1/4-20 bolt and nut with a good sized fender washer backing it up. Be careful when drilling, as there can be plumbing, wiring, or metal structural members under the plywood you don't want to drill into.