Steven has a crazy post about what to do if you have to fight a terrorist on a plane. And I have some crazy reflections:
Sounds to me like the best attack is just the shield rush. Heck, just call out the instructions if the guy(s) only has a knife: 'Everybody pick up your seat cushion and rush the bastard.'.
Good idea about liquid. Get some in your mouth nothing. Send people to get hot pots of coffee and scald the SOB, preferrably on the face.
And remember, I object to violence in all forms. Ahh, the joy of contradictiory human existence. That is all.