Shopping malls in cities, major bus and train stations, gas stations, and many towns along main highways have public toilets. Look for a blue sign with white figures (ladies and gents) for directions to a public toilet. New Zealanders often use the word "loo," or, better yet, "superloo."
Most New Zealand public restroom facilities are clean and tidy and often have a separate room for mothers with young children.
Some gas stations, shops, and hotels have signs stating that only customers can use the restroom. Kiwis are generally fair-minded folk, so if you're genuinely caught short and explain the situation you will probably not be turned away.
Most gas stations in New Zealand have toilet facilities, but their standard is varied. As a rule of thumb, the newer and more impressive the gas station, the cleaner and better the toilet facilities.