I've been using a wired [Kinivo ZX100](http://www.amazon.com/Kinivo-ZX100-Portable-Rechargeable-Resonator/dp/B004HHICKC/] and my phone for the last few years. It's cheap, has great sound for the price, and charges via Micro USB like a lot of modern phones. It's a good kit for GMing away from home.