A variety of activates are available other then surfing, most require an additional fee for participation.  Options include:
Trip to a volcanoe
City Tour through San Salvador
Tour the San Andres Mayan Temple
Tour a coffee plantation
Motorbike tour through the jungle
Zip Line through the jungle canopy
Skate Park (be careful, you're on a surf trip)
Golf
Fishing
City night life

**Some additoinal activities will incur added cost