Step 1: underneath it all
Tuck the bottom inch of the tunic inside itself. Attach the safety pin to one of the fabric strips and use it to sew the bottom of the tunic together. Knot the ends and cinch to make the base of the bag.
Step 2: full circle
For the strap, place the end of one sleeve inside the other. Use the safety pin and another fabric strip to sew them together, knotting and cinching. Weave the final piece of fabric around the neckline for a decorative touch.
step three: flip side
Fold the top of the tunic over to form the flap of the bag. Find a spot towards the center of the bag, under the flap, and sew on the button with the needle and thread. This will hold it closed.