Hey man Ive worked a lot with lighting for parties we organised in abandoned railway tunnels. Generators are by far the easiest way about it. You dont need to go super big like 3500Watts, you can get 250W halogens that do a decent job. 4-6 of these and your looking good, nicer spread of light than less 1000W lights. Obviously if you can transport a bigger generator then the more power the better. We've got a 6.5KW one, its on wheels but weighs so much. It is possible to get a transformer for a car battery though. Theyre really cheap and work well. The kind of thing that lets you use normal plugs in your car outlet normally comes with attatchments to let you plug it straight to a car battery. We use it for a portable audio system sometimes. Gives you a lot of power, just means putting it back in the car to charge it up again. Not sure how many lights you could get hoked up to it though.