Activities: going to the beach! Amazing and beautiful beaches. If you have a car (highly recommended for visiting Costa Rica) drive to different nearby beaches. I recommend Playa Tamarindo, Playa Langosta and Playa Conchal, my favourites. The sunsets in the sea are simply breathtaking. Great beaches for surfing lessons!
Places to eat: I can't remember any particular places, but you should know that this place is FULL of tourists so try to find local places so it's not that expensive. Also, if you don't eat meat, almost everywhere you cand find casado (mostly rice, beans and salad) and you can order it without meat.