My bags are made of rip stop nylon and are stored in a small nylon bag a little larger than a 2 pound bag of sugar. I have 6 of them. They came from Eddie Bauer, but I don't think they sell them anymore. I am asked all the time where I got my bags.
The grocery store sackers love them because they are clean, easy to load and are incredibly strong. The best part is that I throw them in the washer and they dry in minutes. Studies have shown that reusable bags are germ cities and I don't want my food going into dirty bags. The grocery checkers and sackers tell me most bags are so nasty and stinky they don't want to touch them.
I keep one of the bags folded in my purse so I don't have to use bags when I shop at other stores. They are great bags and would be easy to make.