On Rarotonga, the main transport options are the round-island bus, scooters, bicycles, and rental cars. The bus circles the coast road in both directions, starting from Avarua, and costs a flat NZ$5 per ride. It runs weekdays during business hours and Saturday mornings; there is no service on Sundays. Flag it down anywhere along the road.
Scooters are the preferred mode for most independent travellers — the island is only 32km around and you can cover it in an hour without rushing. Rental is around NZ$35–50 per day. Bicycles are cheaper and work well in the flat coastal zone. You will need a Cook Islands driver's licence (available from the police station in Avarua for a small fee) to legally ride or drive. Drive on the left. Friday and Saturday nights bring heavier drinking, so be careful on the roads after dark.
Car hire is available at the airport (Avis, Budget, and local operators). Nothing is more than 20 minutes away, so a car is rarely essential unless you want to explore the interior tracks or carry a lot of luggage.
Between islands, Air Rarotonga is the realistic choice. The airline connects Rarotonga with Aitutaki, Atiu, Mangaia, Mauke, Mitiaro, Manihiki, Penrhyn, and Pukapuka. The island passes they once sold have been replaced by standard fares; prices vary. Book through Air Rarotonga directly or via your accommodation.
Cargo ships connect Rarotonga with the outer islands, but they run infrequently and without firm schedules. If you plan to get off on a remote island, be prepared to wait days or longer for the next boat. This is an adventure, not a reliable transport option.
On Aitutaki, the island is small enough to cover by bicycle or scooter. Most places to stay offer bikes for hire. On Atiu and the other outer islands, motorcycles and bicycles are available from local guesthouses.