One by one, layer three 10" strips of silver vinyl duct tape onto your cutting board (pay no mind to how sloppy it looks in my picture). They should overlap 1" each, so that you end up with a big piece that is at least 10" x 4".
It's okay if it's bigger because you'll be cutting it down later.
Carefully peel the 10"x4" piece from your cutting mat, then flip it sticky side up. As you can see in the picture, I stuck the ends of the sheet back to the mat so it would stay in place. Layer 3 strips of duct tape onto this piece, following the process in step 1.
This should result in a non-sticky, sheet of duct tape that is at least 10" x 4".
Using an xacto knife, cut a strip of silver vinyl duct tape so that it is 8.5" x 1". Line the long side of your 8" x 3.25" rectangle with this strip, then fold it over onto the other side so that it looks like the example shown here.
Repeat this on the remaining long side of this sheet, as well as the long sides of the 7.5" x 3.25" piece of duct tape.
This "lining" process keeps will keep the edges of the wallet looking clean.
Then fold each rectangle in half afterward.
Stick another strip of silver vinyl duct tape to your cutting board. Using a ruler and a pencil, measure out four 0.25" strips width-wise across the tape, as well as a 0.50" strip.
Using the xacto knife, cut these pieces out, rounding the edges.
(The picture is poor quality, but) i hope it clarifies this step a little bit.)
For the inner pocket(s):
Take a credit card/gift card/ID and trace its outline onto an index card. Cut this out, trimming about half an inch from the top so that you end up with a piece of index card that is shorter than the card you originally traced.
Cover both sides of this piece of index card with silver vinyl duct. Trim the tape as needed.
Take the rectangle that you made in step 13 and stick it onto the lining that you just peeled off, making sure that the edge of the pocket rectangle is aligned with the edge of the larger rectangle. Trim the lining as needed so that you can move the pocket as shown. (If you hold this piece up, the pocket should be able to hang down freely.)
Using the xacto knife, cut two 1" x 3" strips of silver vinyl duct tape. Tape these strips along the bottom of the Nintendo side, making sure to leave about half an inch of space between them at the center so that you'll be able to fold the wallet.
Flip the wallet over and tape the inner, pocketed part of the wallet to the outer Nintendo piece.