Alaska weather varies greatly. On a sunny day in port you might wear shorts and a T-shirt, while the next day in a fjord or on a glacier, sweaters, scarves and mittens may be required. To ensure you're comfortable regardless of what the weather brings, pack your cold weather gear and also several items of clothing that you can either layer for warmth or shed to cool down.
Think about the kind of shore excursions you plan to take and what clothing will be comfortable and appropriate. Also consider accessories you might need, such as hiking boots, ponchos or rain gear, fleece jackets and binoculars. A good quality camera can capture memories onboard and the rare wildlife you might spot on an excursion.
You'll want to bring somewhat dressier items for your ship's formal dining nights.
Pack all of your medications, prescription or otherwise, in a bag you can carry onto your flights. Obtain extra prescriptions from your physician for any medications you are currently taking and carry them with you. A hat, sunscreen and sunglasses also are useful for sunny days and bug repellent will keep the insects at bay.
You can learn more about each ship's dress code and onboard services and amenities by clicking any ship name on the Cruise Ships & Ratings page or by asking your Vacations To Go cruise counselor.