If you haven't already, I would recommed asking what the color shots will be used for. If they want accurate color, Velvia probably isn't the right film. Don't get me wrong; when I shoot slides, Velvia 50 is all that I shoot. I love the intense colors it provides. But to my eye the color rendition of the film isn't very accurate.Originally Posted by arigram
I second the idea that a photographer's vest is a good investment. It's amazing how much easier life is when you can keep so many things at the ready.
I have the Lowepro Nature Trekker AW II backpack, and I love it because it can be adjusted for my height (6'7") and it holds an amazing amount of stuff...but it may not be the right pack for you. Try a few on for size if you can.
Make sure you have a couple of cable releases with you (if you only take one, it's guaranteed to go bad at the worst possible time). Also, you didn't mention anything about filters...a good filter system that includes a high quality polarizer, a graduated ND, a few ND's, and a set of B&W filters would probably come in handy.