if in Hermosa then Vista Hermosa is my choice, awesome lunch and dinner. can't go wrong with a casado. stay away from Backyard for food, it takes very long to get your order (even by Tico standards) and its pricey. if you have a car and want to go opposite way of Jaco, Los Alemendros in Esterillos Oeste (10 min drive) has awesome Carribean/Costa Rican food.
If you are going to Hermosa avoid the north end, that's where all of the tourists hang out. It's, what, 3 miles? of beach, but everyone always clumps up right by the backyard bar. I will never understand this.
Food and drinks. get some ceveche from the guys on the side of the road. AMAZING. Beers are surprisingly the same price in the grocery store as they are at the bar, so no excuse to stay in!