Jamaican Dollars. Many hotels and tourist places will also accept US dollars, but change is generally given in Jamaican dollars. Cambios tend to offer the best rates and can be found in most town, and it's best to exchange cash for a few days at a time as you will lose quite a bit of money if you change back from Jamaican dollars.
The official language is English but Jamaican Creole, also known as Patios is the most widely spoken, although you may not hear any as English is generally spoken in tourist spots. Spanish is also fairly widely known.
+876 for Jamaica, and there are no codes for separate parts of the island. Mobiles are prevalent and mobile numbers can start with any digit but 1.
Travelling off the beaten track can be dangerous in Jamaica so it's important to keep as safe as possible. Most locals are friendly but don't be afraid to spend a bit of money to get out of a bad situation.
UK citizens only need a passport with a six month validity to enter Jamaica, although staying longer than originally planned may land you in trouble.