I recently did a remake of a carry bag into a fanny pack.
A client sent me an email and asked me if I could convert his bag into a fanny pack. At first, I was thinking in a very complicated way, and I thought I would need a sewing pattern, etc. As it turned out, all he had to bring me were his bag, nylon webbings for the waist belt, and some hardware like sliders and buckles.
I simply cut off the existing bag handles (shown on the lower left) and sewed on a new waist belt into the side seams that I opened. Now he can carry a lot of things in it, and he can also make the belt longer using the sliders to hang the pack over his shoulder.
If you have any project like this, please contact me to share your idea with me! I learned that it is sometimes much easier to see the projects rather than just talking about it over the email or on the phone.