You can see how these were made by looking at my instructable https://www.instructables.com/id/Sew-Easy-Fashion-Backpack/
. This gallery is to show you what you can do by riffing on the basic pattern. Just by changing a couple elements, you can create a completely new style.
BTW, if you don't have the time, material or inclination to make your own, all of these are available for purchase on my etsy store, http://artsibitsi.etsy.com
Thanks for viewing.