Beth at LulaLouise writes in this lovely tutorial for making a reversible shoulder bag:

I love how this bag is both casual and streamlined at the same time. It’s put together with only four pieces of fabric and should be easy enough for an advanced beginner to complete. The finished size is 27 inches tall and 35 inches around.

This is a great how-to with tons of pictures and a PDF pattern! The flat bottom makes it look like it would be great to bring to the grocery store. – Link.