[r00fus]

Just buy a 10-20Ah portable battery and you're set for mobile devices. I can weather a 10-12h flight with one of those and my iPad/iPhone. If you have a recent laptop, you should be able to weather 5-8hr for work; I seriously doubt you could get better on even an international flight.

[delecti]

Extra bonus is having the battery available the rest of the time. My phone's battery life isn't quite what I'd desire, so I just keep a spare ~10Ah battery in my purse. It gets used maybe once a week at most, but it's worth it for those occasions.