It is a really good idea to take along things from home to show to your campers. They'll be really interested to see things from OZ and hear your stories. A good idea is to make a scrap book and include things like stamps, coins, post cards, photos, pics from mags or travel brochures, pics of animals and that kind of thing. If you know you will be looking after 8 year olds maybe take an Aussie kids book to read to them.
Aussie Flags and pins are always good and many people swap t-shirts at the end of camp, so take something Australian of interesting with you.
Also see if you can find some fun games, activities, songs to share as you'll have ample time to use them at camp and it will help you fill the moments when the kids are bored.
If you like tea you may wish to take your own as the stuff in the US really isn't that good :) and don't forget your vegemite in a tube!