The website leaves much to be desired, but the JamCorder device seems pretty nifty. You plug it into your keyboard and never think about it again — it records and saves everything you play, automatically.
Sure, you could just record on your phone, but because the JamCorder is always working in the background, it'll capture any greatness you may have done unintentionally and will allow you to stay in flow without interruption. Pretty neat.
$99 on the JamCorder site.