Materials needed: a t-shirt, scissors or rotary cutter, thread & needle or sewing machine ready to sew a straight stitch.
Step 1. Find an old t-shirt and turn it inside out. It must be jersey material (standard t-shirt material).
Step 2. Set up your sewing machine (or you can hand-stitch if you prefer.)
Step 3. Turn the shirt inside out.
Step 4. Sew the bottom of the shirt closed right above the existing hem using a standard straight stitch or any other stitch you prefer. If you want to be careful, you can pin the two sides together first. If you use a straight stitch, go back and forth at the very beginning of your line and at the end of you line to help lock the stitch in place. Jersey stretches so you may accidentally pull your fabric and end up with a stitch that is not completely straight - sewing slower can help that, but for this project it really doesn't matter - your bag will still look great even with a wandering stitch like mine shown below. You can repeat/go-over this stitch to make it stronger if you like.
Step 5. This step is optional. Reach inside the t-shirt and open it a little, then pull the two sides apart down near the bottom of your inside-out bag, so that you can create a bit of an opening. Lay the fabric that you just sewed together so that you have a triangle on the end as the picture below shows. Sew straight across a few inches in (as in the picture) and this creates some depth to the bag so that it sort of has a bottom instead of just closing to a line. This is called a gusset, I think. The further you sew this in from the end, the greater depth you give the bag, but that triangle above where you sew will be inside your finished bag just kind of hanging out in there, and you probably don't want it to be really really big.
Repeat this stitch making the triangle corner on the other side of the bag bottom about the same distance in. You can measure if you want to, but it really isn't necessary - eyeballing it will work just fine. If the two stitches are very different distances in from the end or are very crooked, it could be a little noticeable in the final product, but your bag will still function just fine.
Step 6. Using scissors or a rotary cutter, cut off the sleeves by following along inside the seam that attaches the sleeve to the shirt, so that the seam is no longer on the shirt body. Cut off the collar the same way. After cutting off the collar, cut the neck a little wider or deeper if you want to, but be careful not to cut into any cool design/pattern that might be on the shirt front, unless you don't care.
Step 7. Turn it right-side out. You now have a flexible and surprisingly sturdy tote bag that can be used for grocery shopping or anything else. An adult t-shirt makes a huge bag. The one pictured was an adult large, I think. Child shirts will make smaller bags.
