Ultrabooks: Solution for extended periods away from mains power?

I’m interested to know what peoples solution is for keeping devices like Ultrabooks changed when away from a wall socket. In the old days, people would just buy laptops with swappable batteries…

I feel like it may have been an oversight on my part; the choice between an Ultrabook and tablet with a decent keyboard solution (due to their ability to charge via USB)

bump

You can either get a power inverter or a DC car adapter for your laptop. If a car doesn't work, or any generator, then you can always rig a bicycle. At the gym the bike machines had little computers that let you know all sorts of things, including power output, and I could put out about 90W of power. I hope that's a really low power ultrabook if you go that route

Heh, so pretty much nothing. Hmmm I mean the TDP on these modern Intel Core m's is pretty great!!!
I guess there is the option of a 15 metre extension cord...