Materials are your choice. I learned to make this bag from an on-line tutorial using oil cloth. You could salvage an old vinyl tablecloth--the kind with the flock in the back, or denim--as this one. (I made one for my DH in gray cammo denim) My instructions are for denim or duck fabric, which stand up to much use and many washes.
You will need 2 pieces of fabric 15 x 12 inches. On two of the corners, cut away a 2 & 1/2 inch square--this will make the squared bottom of the bag.
Sew the two long sides, and the bottom that has been made by the cutting away.
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I top stitched all the seams for reinforcement. I cut the fabric with a pinking rotary cutter to avoid fraying. The top stitching can be done easily on the sleeve arm of the sewing machine.
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The bag is empty, so you could see how well it stands with those narrow seams.
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Close up of the hem.
* I employed the same pattern, with a couple of changes.
* I used a double sided pre-quilted fabric--just because I liked it--no technical reason.
* I serged all the raw edges.
* I did not sew the 'stabilizing seams' to make it stand.
* I turned the hem outward so the inside of the fabric could be decorative feature.
* Also used red seam binding tape to hide the serging. The resulting casing was convenient for the 'rat tail' rayon (slippery for easy draw) handle/draw string.
Here it is standing open.