Spend Jamaican dollars, don’t spend US dollars. Although US Dollars (USD) are accepted in certain places on the island, this is mostly restricted to tourist areas or fancy places. Plus it’s a foreign currency so the exchange rate will not be in your advantage.
It’s way more fun anyway to deal with stacks of Jamaican money. The smallest bill is JMD 100 which is less than $1 or €1. When a Jamaican refers to ‘one bill’ he usually means JMD 100. When he refers to 'a grand' he means JMD 1000.

In Jamaica they say ‘dollar affi run’ which means money is there to spend it so make sure you have it within close reach. Have some bills in your hand when you get in a taxi or coaster bus. Because of the amount of passengers and the resulting lack of space , you will hardly have a chance to reach into you pockets when it’s time to pay the fare.

Getting back your change when you do not have the exact amount required for a drink or taxi ride is often an issue. You will get your change, do not worry. It might take a little while though. Somebody might have to cross the street to get small bills or ask somebody. In a bar, you could have easily have finished your beer when the waitress suddenly shows up with your change. The clever way to deal with the change issue is of course to collect JMD 100 bills. Pay with bigger bills anywhere you feel they will have change, such as in a fast food restaurant or a supermarket. Start collecting JMD 100 bills you can spend paying a taxi driver or street vendor who is less likely to have change.

Travelling or walking around with huge amounts of cash is never a good idea. That’s just common sense and it applies to all countries. But you shouldn’t worry too much about getting robbed or having your money stolen from your room.

The safest and most effective way to make sure you have your money available to you is getting it from the ATM machine whenever you need it. Make sure your bank or credit cards function in Jamaica so ask your bank before you leave to clear them for the Caribbean. You will find plenty of ATM machines in Jamaica, even in rural areas. Using the ATM will also give you the best value for money because the correct exchange rate will be applied.

If you do carry foreign currency you can change it at banks, places called ‘Cambio’ or simply on the street. Make sure you have an idea of the current exchange rate. You’ll always pay a premium, just try to minimize it. Don’t change you money at the airport, they have the worst rate ever. 

When in need or out of money, your friends and family can always send you money with Western Union. There’s offices everywhere. More expensive of course, but if you happen to be the victim of theft and have no money or credit cards, it’s about the only option left.