I hope the boy the OP found is OK... What luck he had that you where riding by and able to get medical attention to him.

This also got me thinking that I needed to restock my first-aid kit.

I usually carry mostly road-rash treatments... Disposable latex gloves, bandaids, non-adhesive gauze pads, a few antiseptic wipes, and waterproof tape. My job has me on-call 24-7 so I always have a cell-phone with me, which I think is the most important part if the injury is bad enough that the previously mentioned supplies are not enough to cover it and I can't limp or ride home.