Amazon sells beginner leather and upholstery sewing kits for dirt cheap. They're pretty full featured little kits. And they also sell mystery grab bags of random leather scraps. You actually get a pretty good assortment of leather for cheap apparently. And the scraps are more than big enough for wallets and pouches and things like this.

It's on my ADHD list of things to do. I only know these things because I had to get some upholstery thread to make nylon straps with. Just to sew loops into the straps. A couple YouTube videos later and I had a strap I couldn't break with my own leg and upper body strength, and I'm a guy. So I could make straps this way, or belts, or backpack straps, or anything that needs a strap except for actual tie down straps lol.