I actually used to carry one of these:
But I found - repeatedly - that I'd run into outlets like this:
At airports and outlets like this at client locations:
And the right angle plug would be problematic.
So then I started carrying this:
But the 8' length was too much so I cut it to 4' and put this male plug on the cord:
(Yes, I cut the ground off - I know, I know, shocking)
It's great BUT now I'm looking at this gadget:
And I figure with one of these and that, I'm in great shape:
http://www.amazon.com/Coleman-Cable-6991-Liberator-Extension/dp/B001GLWL0O/ref=pd_sim_hi_5