I like a long sleeve t-shirt and a vest of some type. I wore a quilted vest most of the cruise. As Karen stated, you will need a hat and gloves if you plan on staying on deck. When the ship is clipping along at 25 knots, the wind is chilly on deck.
Karen had posted last month that there were a lot of unprepared people on her cruise. On our cruise last month, there were numerous woman on deck that had on high heels, tank tops, etc. They had to be freezing to death! I might be wrong, but I just don't think high heels are what you want to wear when you're climbing outdoor stairs that are slick with dew or fog. One man had to practically carry his wife up and down the stairs and hold onto her when they were walking on deck, she must have had on 4 in. heels. We never saw her that she didn't look like a fashion plate, tight, tight jeans, sparkly low tops, and the high heels. My husband and a couple of other men were laughing one day that they sure would like to see what she wears when she's at home, if she dressed like that to go to Alaska. HA