The one thing I carry in my FAK that I don't believe has yet been mentioned in this thread is an elastic bandage or two -- awfully good at allowing you to get back to the car after abusing your ankle or knee. Also good at holding a dressing in place, etc. One caveat is that the person to whom the dressing is applied should be conscious and reasonably alert. Tension on these things often must be adjusted to avoid impeding circulation.
Also, paper and pencil. It is a good idea to take notes just in case the situation goes south.