Exit the airport downstairs and head to state run taxi stand. Take a taxi to:
1. Old San Juan - Stop on San Fransisco first for coffee and a Mallorca at La Bombanera (great bakery breakfast place situated in OSK. After walk to the seaside and see el Morro and after the cathedral. (check out neighboring El Convento) Lunch at La Fonda Jibaritto, Cafe Manolin, Cafe PR or Parrot Club. 19.00 each way (allow 2 hours before your flight to return)
2. go to Museum of Art and have lunch at Pikayo
phelana.... I will be travelling in June and July with kids.... I will have a 5 hour layover at the airport. I have seen Isla Verde as a place to go for lunch while on layover. Any suggestions, I have two girls ages 9 and 7, the layover is from 9am - 2pm. I heard that you can check luggage in at the airport at the Baggage Room for $3.00 per bag per day. How far is Old San Juan and how much did that Taxi ride cost?
From a native Puerto Rican, be aware sometimes the traffic can be pretty bad!
Metropol is excellent but that is really Cuban food although very similar to local food. I would try as suggested below Cafe Manolin and also AjiliMojili.
And don't forget have a good coffee after lunch.