30 years ago someone gave me a lot of jeans fabric. I made large grocery bags out of them. They are still going strong. Why do grocery bags HAVE to be washed very often? Mine don't get dirty, but if something spills in it, I'll wash it. All the cashiers at our store know us when they see our bags come out. Just make a pillow case shape, as wide or as long as you want, and then turn the corners on the bottom toward the bottom center and stitch down. Make straps and enclose them in the top hem, stitching twice for strength. I also reinforce the side seams. No rips in all these years. You don't need to buy a pattern for that.