...Wait for it...
Remember that this is in the Pocket-Sized Contest, so vote for what you like.
Step 1: Materials List
-Packaging Tape (or any other kind of tape if you don't care about the wallet being see through)
-Scissors or an xacto blade
Step 2: Cut out two card sleeves from the sheet
Simply cut around the borders of two of the card sheets.
Note that by cutting out a sleeve, you make the middle row of sleeves unusable, as there is only one border in between the two.
Step 3: Cut one of the card sleeves
Cut a rectangular hole in one side of one of the sleeves so that a piece of tape can go on the inside of the sleeve and part of it will stick to the other sleeve when it is attached.
Make sure to put a piece of tape up to the sleeve and check the width so that the tape will fit properly.