Actualy during the day on an Alaska cruise jeans are appropriate (think about the kinds of excursions you will be doing). However, evening dining dress codes remain the same with formal nights (2 if it is a 7 night cruise), as well as semi-formal and casual. Casual means "country club casual" where khakis and golf shirts or shirts w/collars (no t-shirts) for men and nice slacks & blouses or casual dresses for women. At least that is how it was on my Alaska cruise on HAL last year. Of course you always have the option of casual alternative dining spots.