I use these small purses all the time. Plenty big for the essentials: money, cards, mobile-phone, keys and lipstick. Since it always hangs over my neck and shoulder, I don´t have to think about carrying it and leaving it, it´s just there.
So here is an easy how-to on how to make them.
First you need three pieces of fabric:
15×19 cm, 15×20 cm and 15x 21 cm
one 15 cm zipper
ca 2 meters of bias-tape (I use the glossy polyester one)
some fun fabric for the front (this is where you can be creative!)
a sewing machine with thread, but that goes without saying 
Sew the zipper on the fabric between the 15×19 and the 15×21 cm pieces. If you iron down a little fold of max 1 cm, it makes it a lot easier to sew the zipper on.
Fold the pieces, so they are about the same length, like on the picture.
Enjoy creating the front. This time, I chose to use some ribbons I got at Britex Fabrics in San Francisco (my definite favorite fabric shop in the States) Here I´m using the embroidery-foot on the more bulky ribbons. Add a folded bias-tape at the top, to secure the edge.
Zig-zag together with the two other layers. Keep the zipper at the back. It will be easier to access that way.
Sew another folded bias-tape at the bottom. And then start at the bottom of one side, continue o after you reach the top, and sew for 110 cm before you put the other side of the purse inside the fold gain. And sew down. Secure. And you´re done!
Of course, it would look even better with some free-style applique and machine-embroidery on there, so that´s next.
I agree, they are so practical I have made several before, in different sizes, and now I’m inspired to make more!
Wow this is such a cool and easy tutorial….thank you so much for sharing it.
Love, Violette xo