If you have a car/ute with you, and aren't low on petrol, then something like this is a godsend:
http://www.jaycar.com.au/productView...3&form=KEYWORD
For $60 or less you can charge your laptop from the ciggy lighter, or run it directly. Handy when you are out in the sticks. I like this model as it is in a rubberised case, and has a little light that you can cover with a bit of red cellophane, it also has extra 12V lighter sockets which is handy too.