You have lots of good answers already but I'll throw my hat in. Flight nurse and medic here. The priorities are always always always A, B, C. It's nice to note that the patient is posturing and to know the proper terminology for it, but it's not particularly helpful in this scenario.
Is the patient maintaining his/her airway? Yes? Move on to B. No? Open the mouth using a jaw thrust maneuver (c-spine c-spine c-spine) clear the airway with suction (as needed), insert an adjunct if possible, and assist ventilation with a BVM and 100% O2. Rendezvous with an ALS crew and transport rapidly.