Is Kangaroo Island realistic as a day trip during five days based in Glenelg?

If you decide to take a car to the island, confirm ferry space and the rental company's island and ferry policy before booking either one. Build in weather and return-travel buffers.

For a simpler car-free day, explore the city and coast by public transport, then book one guided regional outing. That avoids paying for a rental car that sits unused most days.

Kangaroo Island is large and the ferry journey uses a sizeable part of the day. If the island is a priority, allow an overnight stay rather than treating it as a quick Adelaide excursion.