So. My little sister requested this bag for her birthday. I had made myself one, and she liked it so much that she wanted her own. Here is the finished project:
Alas, I did not create this pattern. This person did. I just changed the colors and made it a little bit smaller. But it has such a fun outcome that I wanted to share the pattern. This bag is ridiculously simple and fairly quick to make. It only took me a few hours. As I said before, it is made of granny squares. If you don't know how to make such a square, this is the best tutorial I've yet seen for them. I thought about making my own, but if it's not broken, why fix it? This is actually the tutorial that refreshed my memory after many years respite from the square of granny. Granny squares are probably one of the easiest things to crochet after a straight line.
You can line this bag with fabric - and you probably should, but I do not sew. That is one skill I have not yet mastered. If you have, then, by all means, line this bag and make it stronger. Just keep in mind the very hole-y nature of granny squares when you choose your yarn and fabric. Don't choose a white yarn and a super brightly colored or patterned fabric unless you really want to see the fabric through the bag.
Now, I did the straps a little differently than the original poster did. Here's my "pattern:"
1 - 2. Sc in each st around twice, with sctog in each of the corners. By "corners," I mean these parts. Connect with a sl st after each round.
4 - 5. Sc around in each st and ch, sctog in the corners. (Twice - once for round 4, and once for round 5.) Connect with a sl st after each round. Fasten off.