If you've been cutting up a t-shirt and you have the bottom hem lying around uselessly, here's something helpful to do with it. :3 Mine isn't quite as long as I'd like, so I'll probably replace this one when I get a very large t-shirt.
Cut the bottom hem off a t-shirt and cut the sewn edge out so you have a long continuous tube. Now thread the cord of your headphones all the way through it and add a safety pin right up against the cord just far enough past the end so it can slip over the plug and protect it, but won't slip off.
Now you can stick your earbuds in your purse/backpack/satchel/mouth/pocket and they won't tangle as easily!