I hope you're taking the 8 hr. White Pass RR trip. We took the 3hr. one, and after about 30 min. or so it was very boring. I understand the longer trip is better.
In Juneau we really liked the Orca Point Lodge whale watch and salmon bake. The bake is at a nice lodge, and you eat inside which can be a bonus if it's cold and rainy as it was the day we were there. We saw lots of whales, seals, otters, eagles and other sea life. The boat was large and comfortable with good narration.
I took the helicopter ride to the Mendenhall glacier at Juneau. You fly there, walk around a bit on the glacier, then fly around the other side of the glacier. Depending on how fit you are you can do the glacier climb as well. Both would be good for nature photography.
Personally I am a fan of getting away from the cruise crowd when possible and doing things on my own away from the "prepared" experience. I like to go off on my own with the camera and get the side of Alaska that is not on the tour. The tours do show you some amazing sights, but they are the sights that hundreds of thousands have already seen.
If you are able bodied I would get off the boat in Ketchikan and start walking. There are many photography opportunities when you get away from the crowds along the dock and Creek St. Stop into the visitors center on the dock and pick up a walking tour map. The while doing the tour if you see something interesting up a side street. Go check it out.
There are some really interesting things to do in Fairbanks but I think you are stuck choosing things offered on your tour. The riverboat and gold panning are fun in a Disney sort of way but I love any chance to pan for gold... I've got the fever. That sparkeling metal is magical when you see is appear in your pan.
As for the photography. Pack heavy. Bring all the gear you can. I like to walk about towns with my 24-105mm lens but the big gun 100-400mm is great for catching wildlife from the balcony or deck of the ship. Many people like to take ultra wide lenses but I have not found enough use for my style. There are plenty of grand vistas but they are often so far away that even 24mm is wide enough. Whatever you do keep your camera with you at ALL TIMES. Keep your eyes on the water and shore. Most people do not see the wildlife because they are not patient enough and when the opportunity presents itself you need to be ready with your camera.
If you are into photography or not this is a must. My husband did not carry a camera at all and loved it. Our guide was the best offering so many suggustions for a perfect picture. Whales are a bit tricky to shoot for the first few times and you are given instructions and tips how to improve your techniques and shots. Lots of whales, lots of seals, eagles and the visit to Mendenhall glazier on this trip was amazing. So many opportunies for the best pics...a once in a life time shoot. Don't miss it. We did a back to back last summer on the Island and also did the evening whale watching. My husband again who does not shoot pics at all was the only one on the boat to see a humpback breech and he got wet. he was the envy of the ship.
I also snorkelled in Ketchikan, and we did the 4 wheel mules , the is a second must.
Skagway, we did the jeeps..least favourite, and the eagle preserve rafting( that was just okay)
Kayaking in whittier is also a must , I just loved kayaking in the misty rain, with the mountains ....I will never forget the excursions.
That is what Alaska was to me...not the ship at all.