I have a little dictaphone and if a sound takes my fancy or if a lyric comes to me in the middle of the night I'll just record it there and then.
It's a wonderful thing working with young actors. I know a lot of people don't like working with children. I actually adore it, because you watch their imagination open up and you watch them start to learn this job that I've been doing for so long. They come with such a lack of cynicism.