First item- safety glasses/goggles. Then small hammer, good set screwdrivers, combination and allen wrenches. Needle nose, snubnose pliers as well as side cutters and a pair of nippers (end cutters). A pair of channel locks and a crescent wrench. And since he's only 11 (and lacks hand strength) a pair of vise grips, in both needle nose and blunt tip. Kids love a good magnifying glass! Lumber pencil/sharpener/sharpie and a small scratchpad. He'll eventually need a razor blade but you may want to wait on that one for now.
The possibilities are endless...
IMO save the cordless drill/screwgun, saws, etc. for another time.
Most important thing for a boy with tools is a mentor!!
Even if you have to make up a few projects like changing switchplates or "fixing" mom's cabinets by tightening some hinge screws, do it. And ask for his help! (My son loves to help but not as hot on me saying I want to teach him how to do "X".)