"
there wasn't a whole lot to do" is kind of Australia in a nutshell. There tend be cities or centres of 'activities' with organised tourist attractions / things to do and then vast swathes of 'nothingness' that is fantastically remote or wild. I far, far preferred the nothingness that was full of hiking, geology and wildlife.
KI full or 1/2 day hikes if you can drive your hire car / camper on gravel: Ravine des Casoars. Day 5 of the wilderness trail: Kelly's Caves to Hansen Bay and back (18 km return). Snake Lagoon hike to the beach (corrugated gravel to Snake Lagoon, you can walk all the way from Flinder's Chase NP visitors centre). Unfortunately the Cape Gantheaume trek is closed. There are shorter hikes in many of the conservation areas: https://www.parks.sa.gov.au/find-a-p...angaroo-island
November might still be a bit cool for snorkelling, but there are organised swimming with seals / dolphins tours, snorkelling is calmest on the northern coast. Koalas are virtually guaranteed in the west (Hansen Bay, Western KI campsite or Flinders Chase NP) and kangaroos and wallabies around dawn and dusk and goanna (lizards). There are the seal and sea lion viewing areas. There are pelicans around Kingscote. There are also lots of foodie / wine / beer places in the east.