Friends that I go camping, hiking and on beach holidays with always bring along the speakers. They've just invested in the UE Roll 2 speakers by Ultimate Ears. They're pretty rugged as they get lugged about in a backpack. they're also waterproof. One of my friends travels on business like you and she takes these speakers with her in her suitcase.
It's round speaker, like a disc and has a great, crisp sound, it weighs 11.6oz and measures 5.3 x 1.6″ - I'm not sure if it's the type you were looking for, but it's a starter.