The $9 helmet headset kit from office max. Fits like nothing is there and sounds great.
In past years I have done everything from drain my phone battery by listening to mp3's to getting an old old ugly mp3 player and taping that to the scooter. I think this is probably going to be a bit easier solution but it may be kind of a hassle with the cord hanging down. We'll see.
As luck would have it I just upgraded my phone to a Nexus 4 and I still have the old phone sitting around so I'm going put it in airplane mode and listen to music on that thus saving my new phone's battery for things like navigation and not being able to find a t-mobile Network.
Packing gets easier every year. It seems all you really need is a toothbrush, phone charger, change of clothes and rainwear. Everything beyond that is just added weight. I enjoy having my rainwear bundled and strapped in front of my scooter so that it breaks the wind a bit and makes me slightly more aerodynamic. But I really like to be able to ride the scooter like I do everyday and not like I'm driving a huge bike with tons of luggage strapped to it. This year I have the back rack so I'll be able to strap my backpack to that and be on my merry way without having to worry about being able to fit on the seat or sliding my gear off the back of the seat while I'm riding.