Small pocketknives. Of very little use to terrorists to be honest, their biggest weapon on 9/11 wasn't the "boxcutters" (which probably didn't exist), it was the concept that you should just sit on your butt because the terrorists are just going to try to get a free trip to Cuba or something. Knives or no knives, not much to do against a plane full of angry people hoping that they make it home to their family alive. That and the cockpit is much less accessible.