On a previous flight, I ended up sitting (in business class) next to a federal marshall who transports criminals. Their modus operandi is that the prisoner has hands and feet chained together such that they're not moving very fast. The officer who escorts the prisoner is armed. Any gun on the plane, in any capacity, is a potential terrorist weapon.

Likewise, a power cord from your laptop can also be conveniently turned into a garrot. It's not exactly a force multiplier like a knife or a gun, but it's something.

A broken wine bottle, with all those handy glass shards, makes for a fine weapon. The unbroken bottle, by itself, makes for a handy bludgeon. I'm sure plenty of other suitable blunt weapons would sail nicely through security (e.g., a camera monopod becomes a handy quarterstaff in a jiffy). And, of course, somebody trained in the martial arts can do all kinds of damage.

Personally, I'm wondering if I can go out and get myself a new toe-nail clipper with an attached nail file. I had to break off my nail file folowing Sept. 11, and I wouldn't mind having one back again.