The Cannonball Cafe inside Fort Charles at Port Royal is a simple, reliable place to eat while visiting the fort — serving local Jamaican staples (jerk, fish, rice and peas) in the shade of the 17th-century fortifications. It is not a serious restaurant but it solves the practical problem of what to eat after walking the fort in the midday heat.
The fort visit and a meal here, followed by cold drinks at one of the Port Royal waterfront bars before catching the afternoon ferry back to Kingston, makes for a complete half-day excursion. The Cannonball is better than you'd expect from a fort cafe, and the setting — inside the walls of a British colonial fortification built in 1655 — is hard to match for historical atmosphere over lunch.