I can't put it better than John W. McDMermott in his book "How to Get Lost and Found in the Cook Islands" which inspired my interest in this Polynesian paradise
"Basically all you need to know or have in the Cook Islands is a sense of humour, a pair of old comfortable shorts, a passport and money".
But here's a bit more detail....
As long as you're staying no more than 31 days (90 days if you're a New Zealand citizen), your valid passport is the only entry permit you need, along with proof of onward journey, the means to support yourself while on the islands and somewhere to stay. And you can sort out the accommodation on arrival.
You can stay for up to five months more, but you'll need to extend your entry permit - at the Department of Immigration in Rarotonga. New Zealanders can apply for a three month extension and other nationals for a month at a time. In both cases, you pay a fee for the privilege
From June to September, the days are usually warm and sunny, but you might want a lightweight sweater or jacket at night because it can get chilly sometimes. From December to March, it's a bit hotter and more humid. It also rains a bit more, so maybe a brolly will come in handy! As a general rule, dress is casual except on Sunday (see Religion). I ran into the New Zealand High Commissioner one day in a cafe in town (as you do!) and his choice was a Hawaiian style shirt and shorts - in case that's any guidance!
The Cook Islanders are eastern Polynesians of the Maori Race who are British Subjects and New Zealand citizens. The language is Maori but English is almost everyone's second language. The islands are a democracy based on the British Model.Don't be surprised to see locals - male and female - wearing head dresses or eis, or maybe just a flower behind the ear (an indicator of marital status)
There's lots of it! In the majority of islanders are Protestants of the Cook Islands Christian Church (CICC), inheritors of the London Missionary Society who brought Christianity to the islands in 1821. Almost two thirds of locals belong to the CICC, 15% are Roman Catholics and the rest belong to the Seventh Day Adventist Church, the Church of Jesus Christ of Latter Day Saints, Assemblies of God or Baha'i Faith. Locals wear their best clothes for church - women often in white, light dresses and men in shirt and tie. The churches are filled with glorious singing you have to hear to belive and you'll be amazed at the hospitality shown to church visitors
Tourism generates nearly 80% of gross domestic product. Other mainstays are agricultural and financial services. For many years, black pearls were the main export, but the industry is currently in decline and fishing has now taken the top spot. The distinctive stamps and coins of the islands, which are much sought after by collectors, also generate a healthy income. The $3 dollar note is particularly prized and a very popular souvenir. Cook Islands notes and coins have the same value as those in New Zealand but they're not legal tender outside the Islands
A bottle of Noni Juice makes a souvenir to dine out on (and with?) Locals will tell you it's really good for you...and it's a taste to remember! "Perfumes of Rarotonga" will help you remember your visit with a treat for the senses. Visit their store in town or go to their "factory" where everything is done by hand
And of course, stamps...a visit to the Philatelic bureau in town will overhwelm you with choice even if you're not a collector