Outdoor portraits help

I'll be tackling my first outdoor senior shoot in a couple of weeks, and I was wondering what would be appropriate to bring for lighting gear. Can I get by with a single large 5-in-1 reflector, or should I consider renting a powerpack type system? I have two AB800's but would have to run extension cords to my car seeing that I don't have portable power.

Also any other tips for outdoor portraits? I know to find some shade, or if not possible then have the sun behind the subject for hair light. Your advice would be greatly appreciated.

Thanks,

Gene

P.S. I'll be using a Rebel XT, with 17-55 f/2.8, 24-70L f/2.8, and 135L f/2.