Do you keep a sketchbook? Right now I have nine sketchbooks on the go, which might be a bit overkill.
But each book has a different purpose. They're different sizes and different types of paper. One of them is nearly filled and two I recently started for very specific projects -- one dedicated to color and the other as a garden journal.
I think one of the reasons I have so many different sketchbooks is that I've been chasing the myth of the Perfect Sketchbook.