If you're going to fish with Dave he will probably supply the flies. If you are planning on fishing on your own you should start cranking them out now because you will loose a ton of them to the rocky bottom. IMHO if you're not losing 10 flies a day there you're not getting down deep enough.
Hopefully you will encounter some crappy weather and chrome while you're there. I had my best day on the river last October in a snowstorm - 2 cars in the DSR lot....but many, many bright steelhead to play with