New Trent Easypak 7000mAh Portable Triple USB Port External Battery Charger/Power Pack for Smartphones, Tablets and more (w/built-in USB cable)
New Trent batteries are lifesavers. I keep them in my carry-on and frequently end up sharing with other passengers.  I have never been disappointed and always amazed that I can power up my iPad 3 from zero to around 60% with one battery charge.