Hello littleunknown
As the owner of a Powertreveler, I saw your question: I charge my iPad and iPhone with it. If you can also charge your Macbook Air with a USB connection, that works (but only 3A x 5V = 15W max). Alternatively, I also charge my Macbook via the cigarette lighter supplied (known from cars). There are also rechargeable batteries that you can charge and then plug your Macbook into like a wall socket.