I always have a reusable shopping bag in the bottom of my handbag. The one I've been using finally died, so I made up a new one from an old t-shirt.
This is really simple and quick and a great way to give new life to an old t-shirt. The jersey makes the bag nice and stretchy so you can fit a lot into them too.
T-shirt Shopping Bag
An old t-shirt (or a new one)
Turn T-shirt inside out and sew bottom of T-shirt closed, using a wide zig-zag or a serger. I curved the corners on mine because I thought it would look nicer, but you don't need to.
Lay it out nice and flat and make sure the seams are straight, particularly where the sleeves are. A lot of t-shirts have wonky seams.
Cut the sleeves off and then cut around the neckline. This will create the straps for the bag. Check that the opening is big enough. If it's a bit small, lay the t-shirt down again and trim the neck slightly larger. Cutting it deeper is best, because you want to keep the straps nice and wide.
You can call it a day if you like, or for extra strength, sew over the seams from the shoulders and a couple of inches down the sides to reinforce them. I like to do this, since I have cut into the seams and I don't want them coming undone when my bag is full of goodies.