I put all sorts of goodies into my books, from doodles, color scheme ideas, magazine clips, cards, etc. I was taught to make what are called "thumbnails" to map out compositions before going to the final stage. So my book is full of these little boxes with little compositions in them. This is now a habit I enjoy and helps later down the road when I have a idea block. I can just flip through this book and find an idea I've yet to work through. I really like the Popsicle idea.