Front rack long ways bungeed on. If it is raining I keep the fly and footprint rolled up on the outside of the bag so that at least the inner is mostly dry when I take it out again. Those are going to be wet no matter what, no sense in wasting time or effort trying to dry it.
In rainy places, I also take an ultra-light tarp with me so that I have a place to eat and pack when its raining. Its extra weight, but makes everything a thousands times more comfortable (and therefore enjoyable).