It's cheap, it's easy, and you'll never cry if you wreck it. It's the Jack Bag!
Step 1: Tools & Supplies
Tools & Supplies:
Stuff not pictured because I'm disorganized:
Iron-on patch compound
Step 2: Make a paper stencil/guide
I ended up with the front and the back (the rectangular pieces) being 11" x 13". I also rounded the bottom of this piece for purely aesthetic purposes.
The long strip that connected the front to the back (and makes up the bottom and sides of the bag) was 3" x 36" (I cut it extra long; better too long than too short).
When I was satisfied with the dimensions, I cut the model apart so I could use them as a pattern on the cardboard.
Step 4: Start assembling
Starting at a seam, use duct tape to attach the thee pieces together. I used two ways to join the pieces at the curved sections.
At spots where the curves were, I used skinny pieces of tape so that it could follow the curve (I included that in one of the pictures).
Step 5: Make the flap
Cut the paper guide down just a tad so it is smaller than the main body of the bag, trace it out onto cardboard, then cut it out.