A pair of scissors, a crochet hook for dropped stitches, a yarn needle for joining ends, a knitter's abackus-style row-counter bracelet, a notepad and a retractable pen.
I generally carry 2 projects in case I should hit a snag with one, or get bored with the other (but then again I have like 4-6 UFO's {UnFinished Objects} at any given time).