There's a reason my first post is about writing notebooks:
How can you write if you don't have something to write with and something to write on?
I have carried around some form of notebook since I was in 8th grade, and it has been one my best weapons against writers block.
My notebooks are a sort of creativity dumping ground. I write down story ideas, little details, something neat that I saw, a cool phrase I overheard, or even just how bored I am sitting in class. I like to use the back of the notebook for titles, and those have become my favorite thing to jot down. Even if you never end up using anything from your notebook directly, its a great way to get the spark you need when you're completely blank.
I sometimes use creative writing notebook for businessy things as well. I jot down random ideas I have about marketing my writing, or a new outlet I hear about, or a new idea I hear about how I can make money with writing. Then I usually transfer this kind of information to a more organized list later. But for those random times when you hear about a neat opportunity, its always good to have a consistent, convenient way of recording it.
The notebook idea is useful to more then just writers. Wouldn't it be useful for an artist to always carry around a sketchbook? I can even see how it might be helpful for an actor to carry around a notebook to write down the small, significant details they observe in people going about their daily life to use later in their work. And it doesn't have to be an expensive, heavy, leather-bound thing either. Your kids old notebook from second grade works just as well, or even a few 3x5 cards you carry in your pocket. Or if your one Whatever works for you.
Just remember to always have it with you. At work, school, shopping, by your bed, wherever you go. When that sudden spark of inspiration comes, you'll be glad you did.