My senior year of high school, my roommate and I stumbled on [this tutorial][http://www.wikihow.com/Make-a-Hollow-Book] on making a hollow book. We decided it would be pretty cool to have one, so I pulled a book that I had already read off the shelf and we got to work. We finished cutting it up and gluing it that same night.
At first we used it to store our contraband - Nothing really bad, our high school didn't let us keep things like matches or extension cords in our rooms, which we thought was ridiculous.
Now that I don't really need to hide that "contraband" anymore, I use it as a toolbox.