Portable Power: Extended Travel Battery w/USB port
You can never be sure when flying if your aircraft will be equipped with in-seat power, especially in economy. Generally a laptop's battery only lasts a couple hours when playing movies, but most external extended batteries have been bulky and require another external charger. The recently released Universal Notebook Batteries by APC finally solves that problem.
The APC Universal Notebook Battery is very light and very thin using lithium polymer batteries and it requires no extra charger. To charge up it just plugs in-line: wall plug >> laptop power supply >> APC battery >> laptop. Both the laptop and battery get charged simultaneously. The battery also has a separate USB-charging port for your phone, iPod or any other USB-charging accessory, like a GPS. Best of all it will keep a laptop playing movies during a long flight.
The batteries also come with tips for several hundred specific laptop models so you can figure out how to allow the battery to be charged in-line with your laptop cord. The APC battery has an Apple G4 connector, but currently does not offer an Apple MagSafe connector.