The handwritten pages make for fun giveaways. If someone reviews one of my books online, like on Amazon or Goodreads, they can notify me through my web site, and I'll send them an original page. They can see my creative process in all its scribbly glory.
I included receipts, faxes, newspaper clippings, all sorts of things. I've read novels composed entirely of emails or letters, but not assembled across this kind of mix of materials. I wanted to create the feeling of a detective going through a box of clues.