We did a land trip to Alaska and did one of the one day wildlife glacier cruises and honestly it was everyone's least favorite part of the trip so I don;t think you are missing much. In Seward we did a half day sea kayaking trip that was amazing with this company
https://www.kayakak.com/
We also did a helicopter trip to go dog sledding that the kids (age 14 and 12) loved. there are a few companies that offer that and I honestly can't remember which one we used. We also did a half day fishing trip that was a dud - water was very rough and fish were not biting. We did another one day fishing trip on a river that went better but that was out of Anchorage. We were there in late August and it was cool and there was a lot of light rain. but if you have rain pants and a rain jacket, it is fine. By then there were no mosquitoes, which was a huge plus.
From Anchorage we went to Chugach State Park on our own and rented sea kayaks from a place there (I would google whether the rentals are available in Sept) that was beautiful and if it was anywhere else people would drive or fly hours to get there but of course in Alaska it is just an average park!