The most typical dish in all Costa Rica is "Gallo Pinto", "red rooster", a rice and bean dish served with breakfast and sometimes lunch. Different recipes include herbs or garlic, but the basic ingredients are always black beans and rice, bell peppers and onions.
Don´t pass up an opportunity to try Lizano, the Costa Rican imitation of English Worcestershire sauce. This piquant blend of vegetables, chiles, and sugar is used on almost everything, like ketchup. If you get addicted, it´s now available in the US on your grocer´s Spanish food shelf.