Yami Yamauchi has an Origami model called "Jacob's Ladder". There is a variation called the "Magic Wallet", but I found the instructions to be complex and the final piece allows the contents to slip out. I've revised the model to add a pleat to the top and bottom so contents are held securely in place. I've diagrammed the revision, which I'm calling "Jacob's Ladder Envelope". The diagram shows how to build the envelope with 8.5 x 11" paper to perfectly hold credit-card sized objects. This revision is also thinner, has nicer looking edges, and introduces two new pockets to the outside of the envelope.
Please try it out and and share your experiences. I appreciate any feedback. I've uploaded a video of myself demonstrating the envelope to YouTube.