The Samoan currency is the tala (also known as the Samoan dollar), which is made up of 100 sene (cents). The note denominations are $2, $5, $10, $20, $50, $100. All major foreign currencies are exchangeable for tala in Samoa. For a quick conversion, think two tala to the Australian dollar.
Fijian dollar notes are available in $2, $5, $10, $20 and $50. There is no limit to the amount of money that can be taken in to Fiji (although there may be a limit on how much you can take out of your home country). An Australian dollar buys about FJD$1.50.
The currency in the Cook Islands is the New Zealand dollar. You may receive strange shaped coins occasionally (Cook Island currency) – these can only be used in The Cooks – once you board the plane they become souvenirs. And you may like to pick up a three dollar note as a souvenir.
In Vanuatu the currency is the vatu. Australian currency is widely accepted in Port Vila. One Australian dollar buys around 80 vatu. For an approximate exchange rate, just move the decimal point – so, 100 vatu = $1 and 1000 vatu = $10 etc. AU$13000 makes you a millionaire in Vanuatu!
Cook Islands Three Dollar Note from Banknotes.com