These are just like the still-all-too-ubiquitous plastic grocery bags, but they're fabric.
I followed this tutorial and you actually use a plastic bag as a pattern. The instructions are very good and include a pocket so that the bag can be folded up and is easy to keep in a purse or a car's glove box.
Mostly for the sake of the gift recipients, here's how to fold up the bag....
1. Lay the bag pocket side down and fold it length-wise using the edges of the pocket as a guide.
2. Fold it in half, aligning the top of the handles with the bottom of the bag.
3. Fold in half again and then reach into pocket with your hand and turn the whole thing (pocket included) inside out.