The rain in Alaska is usually not buckets (though that's not impossible), more often drizzle or light rain. Take raincoats/slickers, and rain pants (or rainsuits instead of both of the above), plus an umbrella to use on shore. Expect to get wet, and then if you get nice days it will be all that much better! Enjoy!!!
My mother, who has traveled much of the world, still says Alaska is the most beautiful place she has ever been.