On their way to the Bahamas, a large cruise ship crashed and stranded hundreds of people on this Island. The people are starting to form a society and decide they need a new currency.
The leaders decided to use coconuts as currency. On this island they are not particulary common. They can also be used for food and cups to hold water. This makes them a commodity form of currency.
The coconuts will be stored and guarded on a remote island which will only be reachable by raft. This will prevent people from stealing them and causing inflation. The coconuts are very durable and will last a long time.