Pick a good sized book, something that's easty to work with. I chose an old VB6 database book.
Step 2: Layout
For mine, I started at page 60. Turn to the selected page, and make guide lines, about 1 inch away from the edges of the book. These lines will be used for cutting straight. I used a pen and straight edge.
Step 3: Cut away!!
use a very sharp knife (box cutter is advised) and begin to cut along the guide lines you made in the previous step. The best way is to make deep cuts, and not many of them. So press HARD. Once you have cut through about 10 pages or so, remove them from the book, and there will be a hollow spot where the paper once was.
Step 4: Finishing Up.
I only made it through about 50 pages or so, in half an hour. this is tedious work, but the end result is worth it.
Once you have cut away the desired number of pages, trim the edges so they are smooth.
Step 5: Hide your stuff!
Jewelry, SD cards, drugs, illegal floppy disks conveniently labeled as "seekrit disk". You name it, you can probably hide it in a hollowed out book YOU have made. Just place it on a shelf, and your stuff is hidden. (though I did have one person break into my home and steal nothing but books a few years back.)