Hollow books are a classic way to stash stuff in plain sight. Skip the tedious page-by-page razor blade method and speed up your hollow book creation with an oscillating saw.
The problem with "hand crafting" your hollow books is the amount of time it takes. It's tedious to use a ruler and a razor blade to cut through the book page-by-page and it limits the shapes you might create. DIY magazine Make has a tutorial on using an oscillating saw—they use the Dremel Multi-Max—to speed up the process and allow for more complex cutouts.
You'll need a book you don't mind destroying, an oscillating saw, white glue, a paint brush, ruler/pencil for drawing your outlines, and some miscellaneous workshop gear like clamps to hold the pages closed while the glue is drying. The speed boost comes from using the oscillating saw to saw through the pages instead of cutting them a few at a time with a razor. Check out the full guide, in PDF format, at the link below.
Secret Hollow-Out Book Safe [Make]