Florida being a peninsula is extreamly well served with these.  From central Florida both the Atlantic and Gulf coasts are easily accessable.On the Atlantic side there are not only great beaches on the ocean side but as this consists of 'off islands' giving beaches on both sides of a lagoon.  I don't know if you can swim in these lagoons or not.  On this coast there is Daytona Beach which has very hard sand suitable for driving cars on.  Be careful there are places where the sand is churned up, avoid these unless you have a 4 wheel drive.

On the Gulf side the sand is beautifully white and sandy.  Clearwater is a good destination being at the western end of the I-4 Parking is easy, it has a harbour, a pier and the road goes across a causeway which gives very interesting views.  This is a good place to go dolphin watching and to see the pelicans.