We sailed Alaska that very same week about 5 years ago. Summer Solstice falls during that week and you will have the longest day of the year. When were were at Skagway and Haines (sorry to hear they eliminated that port) it never got dark until 11 p.m. A great time to go, too. My honest opinion was it was a lot more formal than most people led me to believe. At least 50% of the men were in a tux and ladies in gowns or sparkling outfits. Casual wear would be nice pants and top, shirt, blazer, pantsuit just like in the Caribbean. My husband wore a chambray LS shirt with tan dockers, a burgundy collarless LS shirt with vest and dockers, etc. while I prefer pants suits, split skirts, slacks etc. For daytime, due to the changing temperatures throughout the day, just layer your clothes; t-neck or golf style shirt, sweater or sweatshirt, slacks, socks and thick soled shoes, polartec lined jackets were great. Don't forget a hat & gloves as you will be glad you brought them while in Glacier bay and if you take a helicopter to land on a glacier. They don't take much room. Do bring a swim suit for the indoor pool and hot tubs. RCI does a very good job in Alaska.