My husband goes through boots pretty fast, so I wanted to come up with something to do with all the ruined footwear that was pilling up when I realized he also goes through wallets petty fast, too.
This was my first time working with leather and I can tell you that although it isn't essential to have all the special tools, it's definitely a good idea and the next time I do this I'm going to start with purchasing such tools.
That being said, if you have leatherworking tools I suggest you use them, if not you can make do like I did.

Step 1: Materials

The first thing you will need is, if course, an old pair of cowboy boots. Try to find a pair with interesting colors and patterns and not too much wear and tear above the ankles. I was able to make one wallet per boot, but this may vary depending on sizes.

Next you'll need some thread that matches your boots. I used a few different colors, but if you want you can probably come up with one good color. Regular thread is ok, but you may want to go with upholstery thread for a tougher wallet.

You'll also need a needle tough enough to handle the leather. I used the biggest needle in one of those multi packs, there are probably better options but that's what I had and it worked OK as long as I went slow.

You'll also need an exacto blade or good quality scissors. I used both, but you could get away with one or the other.

And lastly, you need some things to measure with. A simple ruler and some credit/id cards were all I used.

Step 2: Dismantle the Boot

Take apart the boot by cutting the stitches; these are usually down the sides, along the heel, from one ankle to the other over the foot, and along the sole. There may be others, if so cut them too. You want to have all the pieces of leather separated from each other so that you can really clean them and maximize material use. Most boots also have a fabric lining, I recommend removing that too. Don't throw any pieces away until you are sure of what you are going to use, I ended up using the lining which I initially considered garbage.

Step 3: Clean and Plan

Now that you have all your leather pieces separated, give them a good cleaning. You can simply use mild soap and water or go all out and use leather care products, whatever suits you. Pat them dry and lay them out; now comes the fun but hard part.

Plan out how you will cut and reassemble the leather into a wallet. You may have to get creative since the material is pre-cut into somewhat awkward shapes; at first glance the pieces I had didn't look big enough, but I was able to make it work by adding a decorative piece that made up the difference in size I needed.
For reference, most bifold wallets are about 4 inches by 9 inches when opened. You don't have to go with the bifold design, but it's simple and doesn't use as much material as others, so it's a good option for first time projects. Also, when measuring keep in mind that you will need 1/4 to 1/8 extra for seam allowance.

For mine I did a bifold with an ID flipout. The measurements on mine are 9 in wide x 3 1/2 in tall. ID flipout 4 in wide x 2 3/4 in tall. Card holder 9 in wide 2 1/2 in tall at tallest point and 2 at shortest point.
Keep in mind though that since not all boots are the same size and therefore don't have the same amount of leather, you may not be able to follow my pattern exactly.

Step 4: Cut and Assemble

When making this wallet I found that I didn't have any pieces big enough for the back. It is likely that you won't either; you are free to come up with your own solution but I will tell you how I did it too. I pieced the two biggest pieces together using the decorative part that fits over the top of the foot to fill the gap and hide the seam. This piece had to be cut and rounded to do so, and when I did it looked funny because the decorative holes punched into it ended abruptly. I fixed this by punching new holes with a nail as you can see in pictures 1 and 2.

Carefully cut out all of the pieces and label them if you need to. Begin sewing them together; the order in which you sew the pieces together will depend on your design. For my design I sewed the the three outter pieces together(pictures 3 and 4), then the ID holder pieces(pictures 5 and 6), then the inner cardholder pieces (pictures 7 and 8), and lastly I put the lining in place and sewed them all into one (picture 9).

I sewed it all together by hand by threading two needles on one thread and passing them through the same holes but in opposite directions so that it had one continuous line all the way down.

If you are going with your own design, then you may have to sew it together in another order. Start with sewing portions that will be difficult to reach once other pieces are in place.

When it's all assembled it's probably going to need to be pressed. There may be a better way, but this is how I did it: fill the wallet with cards (junk ones you don't care about), get it slightly wet, bind it shut with tape or string, and give it a good going over with a hammer. You should be able to see it start to crease just a little. Lastly, put some weight on it (a pile of books works nicely) for a day or two. Take of the tape or string and enjoy your new, one of a kind, wallet.

Step 5: Helpful Tips

-When cutting your pieces out I recommend cutting them a little bigger than you need because you can always go back and trim them up later if you've measured wrong.
-If you are making your own design, it helps to test it out by taping it together and seeing if everything fits right before seweing it together.
-To make sure you stitches are straight, draw a line in pencil so you can follow it.
-when sewing thicker leather it helps to pre-punch the holes with a nail, otherwise you might bend your needle.

And that's it! Thanks for reading and if you make your own I would love to see pictures!