Step 1: What you need:
A pair of scissors
2 binder clips
Some duct tape (I was too lazy to get mine out for the picture)
Step 2: Cut the cards
2. Fold the remaining cards in half and cut out the inside. Keep the white border and throw away the middle. (I took this picture after I already finished the project, so I don't have a cut border to show you.)
Step 3: Pile it up
4. Cut some small strips of duct tape and fill in the compartment, pressing the tape into the corners. Trim off any tape that goes above the first card. I used a little bit of glue to keep the top card down too, but it's not necessary.
Step 4: Stash it
The deck looks totally normal in the box and if you hold it in your hand, but it does feel a little light. Stick it in a drawer behind a real deck (to make sure no one tries to use it and finds your stash) and no one will ever think to look in it for your valuables.