I imagine that you have looked at the excursions on the Aulani web site:
https://www.disneyaulani.com/activities/excursions/
I think they have added quite a few since we were last there.
We have gone on snorkeling trips twice, once in March and once in August. The snorkeling trip in August was fantastic, because we were able to see large sea turtles in the water. The trip in March was nice--lots of fish--but no turtles. We tried to go on the whale watching cruise, but it was canceled due to rough seas.
We went on a walking tour to Waimea Falls (by bus out there, then walking to the falls). This trip offered very beautiful flowers, flowering trees, and bushes. There was a reconstructed Hawaiian village, with an explanation of the customs. One could swim in the pool at the falls, but there was a warning sign for leptospirosis, which put us off. However, as an alternative to swimming, there was a fascinating booth where a woman explained various Hawaiian musical instruments, which could be tried.
We also went to the Polynesian Center, which is actually run by the Church of Jesus Christ of the Latter Day Saints (Mormons). This was quite interesting, because they had small villages with shows and activities that represented various Polynesian Cultures (Tahiti, Tonga, Fiji, Hawaii, Samoa, and Aotearoa), an excellent film, a luau, and a show in an open air theater. The last was one of the most impressive performances I have seen. It is quite difficult to see the entire Center in an afternoon--a full day would be better. The bus out there may stop at the Dole Plantation/gift shop. I enjoyed this, but your view may vary.
There are activities at Aulani itself. Of the indoor activities, I liked the cel painting best. Outdoors, we went on a Polynesian sailing canoe, which left from the lagoon. This was restful and extremely enjoyable. The pools and lazy river are great and the lagoon is quite nice--the waters are calm. The adult pool is great, and there were times in March when I had it entirely to myself for a brief period. There is an evening show three or four days a week, with Hawaiian music and Disney characters in Hawaiian dress. Also, there is a fireside talk by "Uncle." This was an excellent performance when we went.
There is a shopping shuttle to Honolulu (I assume it is still available). Also, you can rent a car right at Aulani (from Alamo) and return it to the resort.
The concierge there can provide information on all of the excursions that are available--learn to surf, horseback riding, etc.
The excursions now include trips to Kaua'i and Maui, which sound great though somewhat pricey. We are likely to do them when we go back (at some point).
We did not go on the Pearl Harbor tour, because I thought it would make me too sad. (My dad was a WW II pilot.)