I went railfanning there for the day in September 2010 on the way back from a conference in Orlando. The place was busy and I saw 29 trains from 0700 - 1900. The railfan park is the place to be as they have shelter from the sun and a radio programmed to the frequencies. I can't remember if they had any port-a-potties, but there is a McDonalds within walking distance. As the sun changes angles, you will have to utilize the two grade crossings on either end of the railfan pavilion, but again they are within walking distance and the scanner should give you ample time to make it. There is also a nice old train depot and museum by one of those grade crossing which also makes a nice spot to railfan from in the late afternoon.
As for trains, you will see CSX locals, manifest freight, intermodals, coal loads/empties, rock, and possbly phosphate. There will also be some Amtrak trains.
If you head towards I-95 and Kingsland, GA, you will also run into the First Coast Railroad yard and they usually have a locomotive parked there.
