Saab 9000

The Saab 9000 is the best surf car. Here's why.
It's a hatchback, so you can fit in a 9'6" longboard AND a 6'2" shortboard AAND a 7'2" mid range gun.

It's got a turbo charged 2.3 litre engine, so you can power to the beach in excess of 110mph.
It's got perfect geometry, so when you're blazing along at high speed, it handles great.
It's only got 4 cylinders, so it gets 22-23 mpg city.

It's a little long in the tooth, so it goes under the radar on the road and at the beach.
It's expensive to fix when it breaks down, but because it's the best car ever put on the road by the best automobile engineering firm in the world (the 9000 was pre GM, remember), so it rarely breaks down. They regularly go 300k before an engine rebuild is in order.
Super comfortable.

The best back seat for a child seat; you won't blow out your back putting the little burger child in and out.

See if you can find a '97 Aero.