I cut it from armpit to armpit and set the top half aside for a later date. I then stitched over a small hole that was in the shirt, to make sure that it wouldn't get any bigger. The bottom of the shirt became the top of the bag, because of the already finished hem. I sewed those triangles in the bottom so that it would lay flat when filled with things. The top sides were a little to floppy for me, so I gathered a small bit up and sewed it closed.
For the handles I took the bottom seams that I had cut off of several shirts (from making tarn) and I cut the loops. Now I had long, thick lengths of fabric. So I matched them in color combinations that I liked and braided them. The one on the far right in this picture was braided with 4 pieces instead of 3. Two of the braided sets were blue, so I used them for the tote bag's handles. I just carefully sewed them to the bag.
T-shirt sewing tip: Use a jersey or stretch needle on your sewing machine. It will go around the knitted thread instead of through it. When a needle goes through the knitted thread, holes can form from the breakage. This has happened to me before. Its not fun to make something only for it to be full of holes in a few weeks.