450D & 580EX II off 12V battery
Probably the easiest way would be to use car charger to charge up batteries for all the devices. Should be pretty easy. I imagine you could use 12V to power them directly, but that would require a pretty complex series of inverters and adapters. Depending on how remote you are going, you could get the battery grip for your camera that takes AA batteries. Then you could just bring a big box of high quality AA batteries to last you the whole time.