a piece of leather
thread for leather and 2 needles
a very sharp cutter
drill with a nail on the front
grease for leathers (optional)
You start by measuring and cutting two pieces of leather according to the desired size of the wallet. However you need to make sure that one of the two pieces is one to one and a half centimeteres longer so as to make room for your cash. Then you cut two smaller pieces of leather which you are going to use as your card holders. Then you start bulding your wallet by glueing the card holders to the smaller piece of leather and then you sew it. Afterwards, you glue it to the larger piece of leather.
Then you measure equal distances along the two outter edges and you drill small holes with the nail on the drill (use the nail on the front of the drill to get a better result). Once you've done that you need to get two needles and the thread and start sewing with this pattern: first you pass through the hole the first needle from the right and then the second needle from the left in the same hole, making sure your thread is the same length on both sides. You follow the same routine throughout all the holes.
When you finish passing the thread through all the holes, at the last hole you need to take one of your needles and pass it again through the previous hole so as to have both needles at the same side to be able to tie a knot. After you have made the knot make sure that you burn the thread a bit to avoid possible fray.
An extra tip is to use grease for leathers in order to moisturise your leather and make it softer and waterproof.