If you are bringing a regular camera instead of digital bring a LOT more film than you would normally bring. You will be surprised at how many pictures you will take.
A few suggestions for tours would be a whale watch out of Juneau. A suggestion for this would be with Orca Enterprises Capt Larry. The ships use big boats with a lot of people Capt Larry only takes 20 to 25 people per trip and many of the naturalists from the ships use him.
Another tour, but it can be expensive, would be a helicopter flight and land on a glacier. It is expensive but worth every penny
A trip on the White Pass Railway is a tour that has some unbelievable views.
Visiting the totem Parks in Ketchikan can be very interesting.
When you are in among the glaciers keep your eye on the water line. If you start to see small splashes like someone dropped little rocks look at the face of the glacier over that spot. That is where the face of the glacier is breaking and you will see some great calving. Do NOT try to spot calving by listening to the sounds it will not work.
Whenever you are looking over the water keep an eye open for water spouts. These will be where the whales are. A humpback whale will blow water 30 to 40 feet in the air.
Keep an eye out for Dalls Porpoise they enjoy jumping off the ships wake.
You will see eagles all over. When looking at the mountainsides keep an eye out for white spots moving these are mountain goats and they will be high up many times.
You say the cruise is in May so there will be thousands of waterfalls to see.
Bring binoculars.