The "key" to packing for an Alaskian cruise is t-shirts and sweat shirts and layer your clothing. Pack a few pair of jeans and even throw in a pair or two of shorts, you could see some nice temps. We went in Sept. and had warm enough days to wear shorts.
Be sure to pack some kind of rain gear, you're bound to run into some. Hats, gloves too expecially if you are doing any kind of glacier tour. I never packed a winter jacket just a few sweat shirts and a warm jacket, hat and gloves and I was fine. Also a good pair of walking shoes are a must, something comfortable and warm.