DH and I LOVE Highway 1, otherwise known as A1A. We usually get on it in Jacksonville or thereabouts. If you get on it above Mayport, you can then drive your car onto the Mayport Ferry to cross the river. It is quite fun. I don't know about you, but that's the only time we ever ride a ferry. And it's cheap. We then head on down A1A. We always stop at Guana River State Park. There are three places you can pull over to park. There are hardly ever but a handful of people here and it's right on the road. Park on the right side, cross over the road on foot (2 lanes) and you'll be right on a very scenic beach - it's very natural with sea oats and sea grass growing all over these huge sand dunes. I think it's the "middle" pull over tha's our favorite. After that you're almost in St. Augustine - just a few miles. We like the Bayfront Inn when we stay the night, but of course, it's fun just to drive through. I've eaten at the Santa Maria restaurant and also O.C White's. Both within walking distance of the Bayfront Inn (nice rooms with a pool and hot tub looking out to the Matanzas Bay) and also the Bridge of Lions. You can rent small scooters that two people can ride and it's a lot of fun to scoot around the old streets. Once you leave St. Augustine you can stay on A1A or there are several places that direct you back to I-95. If you have never done A1A, I would strongly suggest that you do it at least once. We do it always on the way down. You really get a feel for Florida that you don't get on A1A. If you do it, I'd love to hear from you on how you liked it.
