I took my mother on that same cruise 10 years ago and scratched one off her bucket list. We had other family on board too, so it was fun. They did a lot more paid excursions than we did, but nothing really stands out other than the train to Whites Pass from Skagway. Be advised it takes most of the day, but is absolutely worth it.
We mostly walked around town, getting as far from the tourist docks as possible. In Juneau we met Sarah Palin totally by coincidence, browsed a used bookstore where I found a book I'd been looking for for years, and spent a couple hours talking with the folks in an art co-op.
In Ketchikan we did a chef's table type meal sitting in the kitchen of a very nice restaurant talking with the staff. My mom knew relatives of the head chef, and it was basically just the two of us sitting around BSing with the staff and occasionally trying whatever they were cooking.
Our ship was only in Victoria for 6 hours at the end of the trip, so we didn't do anything there. We've spent days in Victoria, and I live just a couple hours from there, so it's nothing big. The stuff I like on the island takes more than that to get to and experience. If you have time, and want to see some of the island, rent a car and drive over to Sooke and then up the coast to Pt Renfrew. Most everyone will head for the Gardens if the weather's good, and they are great, but if you have kids and don't want to see any more country, take them to the Bug Zoo downtown. I've never met a kid yet who didn't like that.
We did our trip in high season, mid-July. It rained most of the time, and people on the ship we're kind of upset. I live up here, and know something about Alaska and the inside passage (I'll be in Valdez for the next 2-3 weeks), so it was okay by me. Make sure you take gore-tex and a hat. I liked being able to get out on deck and only see one or two people. Be advised even in good weather if you're on deck at 5 am you'll be a rare passenger and you'll see stuff everyone else will miss.
Let me also add that, if you're from out of town, plan on spending some time in Seattle. You want to take a day or two minimum before you get on the ship to get used to the time and get over any jet lag. It makes for a better trip. And if you've never been up here, Seattle's got lot's to do and see.