A great deal can depend when in May- mid May won't be shorts weather. Later- maybe a day or two- they take up very little room anyway.
Necessary- lightweight lined jacket, knit hat and glove, 2 pair of walking shoes, rain gear, layers of clothes, I am one that never takes jeans- key is quick drying. I also always do my laundry off ship in Skagway- can be done in a little over an hour with their fast propane dryers- nice conversation too.
Greatly cuts down on bulk.