We rented a car for 2 weeks when we went to Port Antonio. Pretty easy drive from MoBay, for the most part roads are great. Heading towards Long Beach from PA the road is more like the Negril area. I wouldn't go without a car there, things are quite spread out. Others have mentioned some of the great outings, unsure if I missed it but rafting the Rio Grande is a very relaxing trip with fantastic scenery.
My tip would be to check out Reich Falls on their "closed" day. Pretty sure that's Monday. We showed up purely by chance on the closed day and ended up with a more personal tour from a very personable and helpful local, I believe his family owned land there.
At Boston make sure to try the jerk sausage - chicken and pork. Delicious.
