1. button magnets with adhesive backs - I found mine at WalMart for less than $2 for 18
2. fabric scraps - I had these on hand, leftovers from sewing projects. If you don't have any, ask a friend that sews or check freecycle!
Step 1: Placement test
Step 2: Attach
Carefully place the magnet on the back of the fabric at the place decided on in the last step.
Squish fabric to magnet so it attaches well.
Step 3: Cut
At this point, if you wish, you could use anti-fray on the fabric, but I opted not to as the adhesive should hold the fabric well enough it shouldn't fray, and anti-fray can change the color and texture of the fabric.