*supple* leather in the 3-4oz range is what i recommend. before acquiring the leather, get a pattern drawn up for the front, back, flap, sides, (and possible strap, which could be a separate piece of leather or made from pieces of leather). a large needle, some stout thread (carpet thread is fine, so is synthetic sinew, and even bowstring fiber). if the leather is extra soft and supple, working the needle thru it can be done with a pair of pliers and nothing else needed. for stiffer leather, you'll need something to prick holes in the leather, which could be as simple as a hammer and nail, or a punch.
that's the pouch basics - proper leather, large needle, heavy thread, pliers, and maybe a hammer and nail punch. one can get lots fancier, but in truth folks back in the day did this themselves and the vast majority weren't artists and so their creations were at least a tad crude but sturdy and durable. dat's where it's at.