It's very simple to sew this kind of a pouch, even those of you who sit next to a sewing machine once year can do it in no time.
Mine was first in a simple square shape but I later on changed it into a half a watermelon slice shape, so Jonč can wear it easier.
Here's what you will need:
2 outer fabric swatches (preferably home decor weight)
2 lining fabrics
some pins, thread and a pen
First you make a sandwich out of (see photos below):
1.lining right side up
2.zipper right side up
3.strap (put it a few cm from the edge of the sandwich)
4. outer fabric wrong side up
sew with your sewing machine's zipper foot and pin the layers together if you are afraid the fabrics will slip aside.
After you've sewn one side of the zipper you do the same sandwich also on the other side and sew it together as shown above. Take care that you tuck the strap between the outer fabric swatches, so you don't accidentally sew over it.
Once you've separated the layers and put together outer fabric swatches right sides together and lining swatches right sides together you should get something like this:
You are almost done! Just sew the opening together (green line), tuck the lining in the bag, put your cars in it and go for a hike. Or put your hiking book in it and go for a drive with your car.