:I've followed links to patterns for grocery bags several times, and :every last one has been lined.
:Why would one line a shopping bag? It seems to me that a lined bag :would be harder to wash.
People who make these things are doing it as an arts & craft project, not for utility. From a utility standpoint, I don't think you can justify making them versus just buying them. A number of outlets offer canvas or canvas like bags cheaper than I could get fabric for.
I buy them from Trader Joe's, who sell an amercian sewn canvas bag of standard 1/6 barrel capacity for like $3. They're reasonably durable, and last a few years. I make an addition: I sew a piece of webbing about
50" long to use as a shoulder strap. I put a plastic buckle in, so the length can be adjusted, and it can be clipped to things. The should strap makes it much easier to carry, and makes it possible to carry six or ten from the car to the house.