We went to Alaska on the Wonder from May 17 - 24th. (A-MAZING week, btw)
Inside, on the ship, I wore capris, tshirts, 3/4 sleeved shirts, and button-down shirts with a tank top underneath. Think of it as being inside a hotel. The first day I had a sweatshirt, carried it around for an hour and ended up running up to the stateroom to get rid of it.
Out on deck, while at sea it a chillier. This is where it got a little tricky. If you are just walking from A to B and passing outside, we did not need a jacket. It wasn't long enough to put it on and take it off.
However, when we were outside trying to spot whales (which I never saw!

), I was happy to have had my jacket with me still from our recent excursion. (We had not made it back to our stateroom yet.) It got a bit chilly out there after a little while.
NOW... Tracy Arm day... The ship is moving and we were at the very front of the ship. It was C-C-C-O-L-D. As in: jeans, 3/4 sleeved shirt, warm fuzzy wintery wait-length coat. However, we were out there for 6 hours. They had hot chocolate, thankfully, but it was cold. Again, front of the ship and moving.
As for excursions and ports: We did steam train, a boat excursion, and a dog-training camp. Inside the steam train, no jacket was needed: jeans and 3/4 sleeved shirt. Top deck of catamaran on boat excursion: a little chilly, jeans and a jacket. Dog training camp: jeans, 3/4 sleeved shirt, jacket, gloves, hiking boots with thick socks, and a winter cap. When that sled got moving, it was chilly.
We had amazing weather with no rain.
Hope this helps,
Dreams