From the research that I have done on the internet recently, the best bait for crawfish is oily fish. Not just any fish, oily ones like salmon, trout, tuna, mackerel and the like. Any fish will work but it is best if it has lots of fat content. This comes from a couple of different commercial crawfishing people so I assume that this is the best information available.
I have also read that there is a commercial crawfish bait product produced by Purina that is similar to a dog buscuit in shape and consistency but is made of processed fish carcasses. My reading tells me that this bait is only effective in warm waters, however, so it may not be viable in the PNW at all except for shallow lakes in late summer.
My own personal experience as a kid says that a good old piece of smoked bacon is just about as good as anything.
I have been saving trout heads and skins from my recent catches and freezing them in ziplock bags in prep for the opening of crawfish season in May. I separate the fish parts by the lake where they were caught because I do not want to cross contaminate the lakes with diseases.
The cast that catches the fish is never too short. Patrick McManus