Benta Falls is a nice quick trip from Negril. About 30-40 minute drive. They're not huge falls but it's a nice chilled atmosphere where you get to lounge in the river and take in the lush tropical vegetation around. If you go there you might also consider going to the Roaring River Cave as it's very close.
Border Jerk is awesome and one of the best if not the best jerk spot in the north coast region of the island. You will pass through some nice little country towns like Haddo and McField on the way. Both have little rum bars that are fun to stop at and get a beer as well as mingle with some locals to get a feel for rural Jamaica. At Border Jerk you walk up to the window, place an order, and pay. Then you go to another window to pick your order up when they call your number. Be sure to keep your receipt. It's a busy place and can get somewhat chaotic so I've had my order crossed before and needed my receipt to straighten it out to get exactly what I ordered. You will see a lot of locals eating there which to me is always a good sign for good authentic food. Be sure to order a side of festival to go with your jerk.