If you have a thing for portable speakers with a slight vintage flair, you might want to check out this Walkman wristlet. Featuring the design of technology from long ago (that's long ago in technology years) this wristlet will hold what you want it to and play your favorite tunes.
I usually scoff at portable speakers a little, but more and more I find situations where I'd love a set myself. I swear not in public transportation or anywhere else I'd subject the public to my taste in music, just in those random situations where my computer is not around and I'm tired of wearing earbuds.
It measures 6” x 4.5” x 2” and is sold in the blue shown above. It is also available for a decent price, being sold for $14. Sure it may not have stellar sound quality, but it works. Just plug the speakers into your MP3 player as usual.