While I have a complete rain suit & hat from the dollar store, most often I just use a large black garbage bag with a slit to poke my head through, and one for each arm. Quick, simple, easy, cheap, light weight, effective, and small enough to keep in my pack all the time.
If I’m going to be out in the rain all day, then I go the full rain suit path. Waterproofing my clothing is more hassle than I wish to deal with.
"Old school, cheap, simple, reliable, and easily replaceable for the win!" ~ Traveler@Heart