This is just a simple cylindrical bag that you could also use to carry a padded mat for camping or really anything that rolls up. You can add whatever designs you want. (You could easily do anyone from the Avengers like Iron Man, Captain America, Black Widow etc.)
About a yard of fabric (the exact amount will depend on what size bag you need, see step 1 for measuring)
Accent fabric or embroidery thread (depends on your design, I only got 1/8 a yard and was covered.)
Pattern making material or poster board
Step 1: Getting Measurements
My mat was 24" long and had a diameter of about 41/2".
To make sure the bag isn't too tight, add about an inch to an inch and a half to those measurements. I cut out a rectangle that was 251/2 inches long and 19" (6" x 3.14=18.84" circumference) wide.