Personally, if there were NO air marshalls, I would consider it open game on any terrorist in reach, and the fight would be on to keep them out of the cockpit using any means available.
The Aircrew of the plane are responsible for flight security, and I would assist them in maintaining the ability to land the plane and control it, because once that is lost, they can do anything they want.
Bottom Line:
1) do anything you can to help the aircrew keep control of the aircraft, and nothing to help the goblins.
2) Hurt the goblins as much as you can..
I've seen numerous helpful tips all across this site so I will add mine:
Being a frequent business traveller, I always pack my power cord for my laptop at the top of my briefcase. The power converter box can be a good weapon when swung, and the cords themselves would be handy to subdue someone. Tied up, strangled, etc.