Only thing that hasn't been mentioned so far is spinal stabilization. If you had proper PPE (gloves definitely, mask preferred given the facial bleeding and coughing) you could have gently stabilized his head and gently prevented him from moving his head/neck around too much. That gives the added benefit of putting you in position to monitor the airway.

There's little else you could have done. Even EMTs have very few interventions available to them... oxygen and an oropharyngeal airway (or King/Laryngeal mask in more enlightened jurisdictions). That's pretty much it. Paramedics can intubate and push resuscitative fluids, but again, that's only a stopgap measure.

Trauma is a sickness and the only cure is the knife. Surgery or death.