I respectively disagree with the basic prowess of this. This is a defensive situation, and should be thought of as such.
Lets think about this realistically. Most likely scenario is a knife/razor/etc.
Swinging a flashlight or sack of coins for a knockout blow requires more room than any plane I've ever been on allows for, even if you get the chance. I guess you could go over the top and hit them on the top of the head, but this isn't the movies and that kind of strike isn't as good as one to the face, jaw, or temple. You're also probably going to give up the element of surprise. The priority is neutralize the weapon first if possible, not the person. Once that's done you have a huge advantage in numbers. Incapacitating someone who is willing to die to kill others with a pen is also not very likely.
Really, the only realistic course of action is to restrain, get rid of their weapon, and choke out and/or having other people jump in. Maybe you can grab their hair and knee to the head which will incapacitate most people, but that's still relying on good luck.
Chances are, you're going to be grappling and for sure playing dirty. This isn't even mma, this is life vs death anything goes. I'd rather bite a mf on the jugular and gouge their eyes out than try for a perfect stab with a stupid pen.
Therefore, what you want to have is as much thick leather on as possible. Leather gloves for sure. Gloves and a jacket with the collar popped with some sort of hat if possible. You're most likely not going to get away unscathed, sorry. In a scuffle with someone with a knife on a crowded plane, somebody is probably gonna get cut. So its about minimizing the chance that that cut disables you. You need to disable the guy(s) long enough to take advantage of your advantage: numbers. If you can grab their knife or hands, fights over.
Anyhow, my .02