Like others here, I have given thought as to what improvised weapons I could employ to defend against an attacker. For this exercise, let's automatically exclude firearms, knives, and any other purpose-built weapons. In fact, let's think of those items that would be allowed into a courtroom or onto an airplane.

Besides the obvious items I might carry on my person that are purpose-built weapons, I can envision using the following items (I also have 4 years of hand-to-hand combat training and a knowledge of "pressure points" that would make these items even more efficient):

Human Brain (always #1)
Fisher Bullet Space Pen (thrusting weapon)
metal carabiner on keychain (striking weapon)
Bandana (swung, loaded with keychain)
tightly rolled magazine (ever see the movie 'The Bourne supremacy')

Other items would vary depending on where you are, and what items are close at hand.

What say ye?