I'm one of those people that carries around a notebook or sketchbook at nearly all times. I once wrote about my totally irrational juggling of 3-4 books of ideas and notes at any given moment, and reasons why I refuse to buy those really nice ones with excellent paper anymore.
I'm working on a few projects- fashion events, private client design, etc, so keeping a pen and paper handy for quick scribbles whenever an idea hits is important.
Sometimes the drawings become the foundation of entire projects, strokes of genius, or just plain bad ideas that need to be drawn out to make room for better ones to come. It's all a part of the creative game.