While surfing instructables.com and seeing the Wallet Challenge mentioned, I thought I would give it a shot keeping in mind my own criteria for any wallet I buy: minimized volume with a priority to minimizing the depth, plus speed of access to the items inside. In two words: thin and fast. The wallet design here provides a home for, if not everything usually found in a wallet, then at least the more problematic---the cards. Credit cards, membership cards, business cards, whatever. Most of the time I do NOT want these things hanging around my wallet, but I want them handy in my book bag or car close by in case I need them.

As I was thinking on this I eventually settled on an accordion envelope with thin material for the accordions and constrained at the bottom to allow it to flex open and display the contents all at once---random access. This is a common design, and if the accordion material is thin enough, it stays pretty thin overall.

The materials used here (paper) were selected for ease of manipulation, but something with more strength or resistance to moisture could easily be used, either for the cover, the inside, or both. Fabric, metal, even panoramic photos could be used for the covers. The interior is best kept thin, and the paper I used could easily gain some moisture resistance from scotchguard. Closing the wallet is also wide open to change. Two closures are shown, but many are possible, especially with more robust cover material.

Final thickness of the empty card wallets are about 0.5 cm and can hold from 10-13 cards.

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Step 1: Gather Materials

Pictured here are all the materials you technically need to make this wallet:

Scissors
Glue (I chose mucilage for its paper-bonding as well as its applicator)
Foldable material for inner accordions. I chose thin graph paper. .25" or .20" squares
Stiffer material for cover. I chose an old brown mailing envelope and a 20lb bond sheet of paper.
Ruler: To measure and as a fold-starter.

Step 2: Make the Accordions

Cut a piece of 8.5 x 11 inch graph paper longways into two strips, each just narrower than a business card is long. Note: the length of the card, determines the width of the 11 inch strips of graph paper. They can be a little narrower than the length of the business card---there will be a little extra room because of the way the wallet will be bound at the base.

Fan-fold pieces along graph lines, every two lines---this is the handy byproduct of using graph paper: built-in guides. This will give you a 0.5 inch deep fanfold (for 0.25 inch graph paper) or a 0.4 inch deep fanfold (for 0.2 inch graph paper). That's probably as shallow as you want to make the folds. Out of an 11 inch piece of graph paper, you get 10 "compartments" using 0.25 inch paper, and 13 "compartments" using 0.2 inch paper, with good retention of the cards.

Step 3: Make Cover and Glue Accordions on One Side

There is a gluing choice to make here: Inside (see the white sample) or Outside (see the brown sample). The easiest gluing method is outside, but the accordion material shows on the outside when closed. The inside gluing method has a cleaner look from the outside, but is tougher to get aligned well. Your choice.

Cut a piece of cover material as wide as the widest ("tallest"? - check the picture) card you will store. For inside gluing, make it, say, another 1/8" wider. Cut the piece about 3 times the length of a business card (front, back, top flap).

Previously, when fanfolding either the 0.25" or the 0.20" quadrille graph paper (of length 11"), you probably ended up with an accordion with one extra flap, kind of like this: /\/\/\/\/\/\/\/, like an "N" with too many middle bits. Cut one of them off so you end up with something like this: /\/\/\/\/\/\/\/\, like an "M" with too many middle bits. This is more or less optional for the inside method, mandatory for the outside method.

Inside: Glue the outside of the last flap of an accordion and align it with the side of the cover at one end. Repeat for other accordion on the other side of the strip, width-wise. If you need to, Place a card to be stored into the compartment closet to the cover material to check for fit. Make sure the accordions are "mirrored", that is, that they create symmetric "compartments" between them.

Outside: Glue the inside of the first flap of an accordion and place it over the cover material at one end. The material itself and the fold help to get perfect alignment. Repeat for the other accordion on the other side of the cover, width-wise.

Step 4: Finish Gluing Accordions

Hold down accordions and fold over the cover material on top of them. I used a pencil to add some play in the cover material, to give it some room to expand at the bottom when there are cards inside. The trick here is not to give it too much room or the cards will not be held in the wallet at the bottom by friction.

Inside Gluing: Apply glue to last flap on one side, align with cover and press to apply, repeat with other accordion.

Outside Gluing: Pull last flaps up and over the cover material. Apply glue to each and press in place.

Step 5: Create a Closure

Keeping the wallet closed can be as simple as a loose rubber band or binder clip, or as complicated as you want. What you use will heavily depend on your cover material. Paper can't take much (e.g. rubber band, tabs), fabric can take a great deal more (e.g. buttons with string, snaps).

For my paper samples, I chose to make a tab for one and a captured rubber band for the other.

Captured Rubber Band: Find a light-strength rubber band that is barely snug around the width of the closed wallet. Cut the cover-flap from the end into thirds width-wise---cut maybe 1/3 of the length of the cover-flap (I cut up to 1/2, but I think 1/3 would have been better). Fold middle tab in half, glue it to itself. Fold again in half, place rubber band in the fold and glue down, capturing the rubber band. Fold side tabs and glue to give it a little extra strength.

Tab: Cut a slit into the middle of the "front", the side covered by the top cover-flap. In the cover-flap, cut a tab as wide as the slit and all the way up to the level of the slit underneath. Fold over and glue as you wish---I made a double-thickness tab with the sides folded over for some added strength.

Step 6: Finished!

Here are some finished pictures of the two sample wallets. Note the white wallet's tab closure (colored red in one photo) and the brown wallet's rubber band closure

Optional: While the wallet keeps cards pretty well in the friction at the base of the accordion, you can, if you wish, add some side-to-side stability by gluing down a extra piece of card-sized paper to one of the "compartments" in the middle of the accordion. You don't lose any storage space and you keep the sides from moving away from each other.