Voltaic has announced at CES a new laptop bag that is solar powered and is able to actually charge the laptop.  Of course, the bag has to be in the sun to do this which I'm not sure how keen I am about that.

But imagine a scenario where you're outside for a long period of time. This would be quite helpful then. At $599, it isn't cheap so you would have to really need this capability to justify the cost.

I'd be more inclined to just bring an extra battery with me. My laptop gets 5 hours on a battery. But at the cost comes down, I could see this becoming increasingly popular.