Power outlets are great, they can deliver power to anything, with the right adapter in case of small gadgets, but they aren't found everywhere.
Since it's particularly annoying for the phone to die on you during a trip, Mophie has released the Juice Pack Reserve Micro, which recharges smartphones through a Micro-USB port.
Of course, anything that isn't a smartphone but runs on a battery and uses micro-USB can be recharged as well.
This is where we would say what the catch is, but there doesn't seem to be one, unless you count the fact that, since Juice Pack Reserve Micro is a portable gadget itself, it needs to be recharged from time to time too (via USB 2.0).
Mophie comes with a key chain loop, stores 1,000 mAh of energy and sells for $40
/ 31-40 Euro.