Ugh. Much as it pains me to give any attention to the litigation-happy Monster Cable (previously seen harassing Monster Mini Golf for trademark infringement and generally overpricing everything), this power adapter looks genuinely useful for the lightweight traveler.
It's a tiny U.S power-strip which triples the available sockets and also adds in a USB socket. This last is essential as pretty much most of what you charge these days is USB, and thus eliminates a whole other box from your luggage. And while you don't see it in the pictures, the third socket is around back, further saving space.
When not in use, the cord wraps around and plugs into itself, keeping a nice tight package. And – amazingly for Monster – it even comes in at a reasonable price: $25. Available now, wherever overpriced copper and plastic cords are stocked.
Outlets To Go Power Strip [Monster via Path Less Pedaled]