The following are instructions to add a handle to my Ditty Bag Pattern.
1) Cut your strap however long you need it.
2) (Optional. You can skip this step if you don't care if your handle is different.)
a) Cut a piece of fabric about 2.5 the width of your strap. Press the edges over by 1/4" and fold it over the strap, pinning it in place.
b) Stitch close. I added a simple zig zag stitch here, because I didn't care about it showing. You can opt to hand sew the strap. Just make sure that you tack the fashion fabric TO the strap in more than several places so it doesn't shift about.
3) Sandwich the handle between the lining and the fashion fabric AFTER Step 4 of the Ditty Bag Instructions, and make sure the ends extend beyond where you want your channel casing to exist. Pin in place. Then, when you sew your channel casing, you will sew your handle into the bag. Just make sure to backstitch several times where the handles are located for extra security. I also added some "decorative" zig zag stitching above the channel casing to provide more security for the handles.
4) When you add your cording in the casing, just make sure to be aware that you'll have straps near the openings and to adjust the cording as needed.
If you have any questions, please feel free to ask and I'll do my best to answer them or to clarify any confusion.