I know the area south of the Carlsbad Airport (my home airport) rather than north. Regardless, here are some suggestions:

1) The Carlsbad Outlet Stores have some good shops. As you drive west to the freeway from the airport, the outlet stores are just north of the flower fields on Palomar Airport Road and just prior to the freeway.

2) You can take Palomar Airport Road beyond the freeway and head north on the Coast Highway. There is a lovely boardwalk along the Carlsbad Beach. Fidels is a nice Mexican restaurant. It is on the coast highway, just south of Carlsbad Village Drive. You can return to the freeway from Carlsbad Village Drive --- or you can continue to drive north to Oceanside.

3) Oceanside has a beautiful long sandy beach, and has a pier where you can walk out over the water.

4) Mission San Juan Capistrano is one of the more interesting California missions. It is well worth a stop. There are pleasant restaurants, including outdoor eating areas, on the street that runs parallel with the train tracks, just west of the train station. This street is a small historic quarter.

5) Laguna Niguel is well known as an artist community. You should be able to find lots of galleries to visit.