I've made quite a few of these as they're really easy to make. You just chose the width to cast on, crochet until it's twice the length you want it to be, and sew up two sides, and you have a bag! Tassles are nice on the bottom, and you can make a strap using icord or other weaving techniques such a plaiting or ones that you may have used when you were little to make the friendship bracelets that your friends never wore :(
You only really need one 50g ball of yarn, and I've used different funky yarns (fuzzy ones, metallic ones, bobbly ones) for different effects. Hopefully I'll get photos of my other creations up here eventually, and I hope I'll get to sell them one day too! The one pictured is the one I use to carry my mobile and/or iPod with me around the house when I'm wearing clothes without pockets.