Jared made fun of me for making a bag out of bags, but seriously, this is a cool idea.
I found the tutorial here. Mine does not look like their sample (mainly because I always stop following instructions or counting when I crochet). You basically take similar colour plastic grocery bags (about 30), cut the handles and bottom seam off which leaves you with a rectangle loop. Then you cut it into 1.5" strips (from fold to fold to keep them in loops). Then you take the loops and knot them together to form a long chain. You can just keep adding the loops as you crochet, as you need them. There are full photo instructions on the link above. I might undo the top two rows of mine and make the whole bag longer and put two longer handles on it for over the shoulder. That's if I feel like cutting more strips out! All in all, I think it's a great way to use all the hundreds of plastic bags I have in my broom closet! Having said that, I do have enough bags for 4 more of these bags!
Another use for the plastic bags, is making material for sewing. Just cut the bag into strips and layer and overlap them. Put them in between to layers of parchment paper and iron them, melting them into one thick piece of material. Then you can use it to sew all kinds of things like this:
Target bags from here.