I make these all of the time. It is super easy- a pleasantly gratifying project. The pouches are fully lined; it can be a little tricky to figure out on your own, hence the tutorial.
First choose coordinating fabric that you like. You will also need a zipper. I chose this super cute Cath Kidston floral canvas and Free Spirit lining. Both are available on Etsy.
I like to use the zipper as a guide for cutting out the pouch, Make the lining about one inch longer than the main fabric. The pouch can be any size that you like as long as it is a rectangle.
Iron the top of the lining fabric over about 3/4 of an inch. This will make it much easier to atatch it to the pouch- do not skip this step!
Sew the top of the main fabric to the zipper, then iron the wrong side up.
Now you will be glad that you ironed! Place the lining fabric over the zipper and sew along both sides. If it is a little uneven at the sides, don't worry- you can fix it in the next step.
Now, turn it inside out and sew around the perimeter, leaving the bottom of the lining open. Leave the zipper partially open so that you can turn it right side out again. It is also a lot easier if you start each seam at the zipper- that keeps it from shifting and... inevitable seam ripping.
Now turn it the right side out. Fold the lining in and sew it closed. I don't mind the seam being visible because it is in the inside of the pouch.
Tada! Wow! It changed colors. That is because the picture I took came out very badly and I didn't realize it until after sundown.
I use these pouches all the the time. My kids even use them to store crayons (for car rides) and little toys.