I find it best to use a Nationwide Card (no commission) and you always best rates... Also simple, no need to keep large amouts of cash in your case/room. Simple! If there's two of you (a couple) then it's good to have a card each (just incase you loose one). It's as convienant as using one in the UK. Well worth it.
Jazz12 - Dare I say sweets arent the best thing to bring for the children... I am sure the children would say it was but you should think about their poor teeth!

- Toothpast and toothbrushs would be a better choice! :o) - I know I'm mean, but it's never good when you have to take the children to the dentist (which they don't really like to do) and they have to have their teeth pulled or drilled...
Pens and Pencils also are what most people generally think of to bring as well.. As such we always get plenty... A pencil probably last a few months with a child, where as a bar of soap may last a week or two.. So more soap the better
Like GFF said there's a good list on our website..
http://www.ChildrenWalkingTall.com/Charity-Luggage.htm