I found this quick little tutorial and made three bags out of Ben's old, stained t-shirts that he was outgrowing.
The shirts were too precious to him and freighted with memories to cut into rags, and too stained to be thrift store donations. I looked at a bag somebody else made that I have and puzzled out the little boxed corner (I don't know the name) for a little fancy extra.
I'm keeping these bags in my shopping cart that I wheel down to market. They are a nice size for keeping produce corralled until I get home and pop it into (reused) plastic bags for the fridge. I'm very pleased (and a little bummed about all the sweet t-shirts I cut into rags).