http://www.eglin.af.mil/news/story.asp?id=123048094
Go to the Jackson Guard office on Hwy 85in Niceville. Sit through a short film on "Unexploded Ordnance and You" (it's really for their liability purposes; as long as you stay on roads and trails, the odds of finding something boom-like are about the same as going to Grayton Beach or Topsail State Parks) show driver's license or other official proof of identity, pay your $7-$8, and they'll give you an Eglin recreation permit good for the rest of the fiscal year and a giant map of open and closed parts of Eglin reservation. The permit cost essentially covers paying for the map.
There are more of less 280K acres of base land maintained for recreation purposes between Milton and Freeport, including a fair amount of single track, creek and river crossings, and unofficial mud-bogging spots. Just respect roads marked as closed because a) there is probably a reason for the closure and b) there are places deep in the pines that are so top secret-like you'll get yourself arrested for going into that closed area. Also note that Eglin reservation is very popular with hunters in the winter, especially during deer season. (That time of year, stick to areas closed to hunting.)
If you're going to be here for a while, it's definitely worth it to get an Eglin rec pass. If you're a short timer, we're also had fun at Pine Log State Forest north of Panama City Beach.