You might want to plug in a USB powered external hard drive
PLUS
plug in a USB powered battery charger to charge some batteries
Will this Apple laptops one USB port be able to handle this load? Using a USB hub of course
All valid concerns, we'll have to wait until the real deal is in people's hands. Are you speaking of charging another device's batteries via the Macbook port? Personally, I don't do that except for a pair of external mini-speakers I use with my old Macbook (I like to crank up the sound for videos and the speakers have rechargeable batteries). I also use external USB hard drives for storing large movie files as well as for backups. But usually have the external AC adapter connected to the Macbook most of the time.