To avoid
Avoid driving at night if you can, as the roads are unlit and the signposting is virtually non-existent. The Costa Ricans are also fast drivers and animals seem to appear on the road from out of nowhere!
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To try
Costa Rican cuisine is rather mediocre and does not really have any distinct national dishes. Most of the dishes are based on beef, pork or chicken, which are inevitably served with rice and black beans (sauces and various vegetables can add a bit of variety). Having said that, the grilled fish is excellent, and sweetcorn is used to make many types of pancake. The authentic Costa Rican breakfast is generous and usually consists of 'gallo pinto', a plate of rice and fried beans eaten with cream and 'natillas', corn pancakes. Dishes from the Atlantic side of the country are strongly influenced by Caribbean cuisine, though this is less true of those from the Pacific coast. One thing you will find everywhere, though, is plenty of fruit, particularly watermelon, pineapple, passion fruit, banana, mango, melon, starfruit and guava, among others. The country's internationally renowned coffee (such as the Tres Generaciones brand, for example) is also consumed in large quantities here, and the rum is of excellent quality. You can also eat here without breaking the bank in the 'sodas', which are traditional little diners that serve a set menu. For a bit of refreshment, order a 'Caïpitica', a light cocktail made using lime and sugar cane liqueur (Guaro).
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To bring back
There is a wide variety of Costa Rican handicrafts for sale (if you look hard enough!) and often at pretty reasonable prices, including gold and silver replicas of pre-Colombian objects, small wooden decorative items, wicker baskets from Guanacaste and leather goods, not to mention the traditional small wooden painted carts or 'carretas', typical of Sarchi, where these traditional souvenirs are primarily produced. The country is also internationally renowned for its rum and coffee, so stock up whilst you're here!