Oxygen
Interesting exchange re O2. The audio selectors were found by the Boeing adviser to NTSB - both undamaged by the impact, not even dusty, and both at MASK.
The Flight Deck valve was about half open. I was taught to fully open it and then turn it back a 1/4 turn (Gorilla avoidance!); am I right in thinking that the flow is quite severely restricted if the valve is only partially open?
Also interesting that the pilot's masks were never found but the supernummary ones were easily located in the flight deck area and in reasonable condition.