This past Sunday I visited the David A. Sarnoff Preserve which is home to 2800 acres of pristine pine barrens. The brush is very thick, so its best to wear proper hiking gear; long pants, sleeves and have tick spray on hand for sure!!
The trails aren't very well marked, and a local guide recommends hikers us MapMyHike or a similar app. The preserve is very quiet and there is a ton of wildlife, but you need to hike quietly. Mid-way through I saw some wild turkeys!

You do need a Department of Environmental Conservation (DEC) permit to park & hike, but both are free, obtainable online from the DEC site. Also, the GPS will most likely not bring you to the actual Parking Lot for the preserve. The map above offers a visual marker. If taking Old Riverhead Road to Quogue Riverhead Road (route 104), the preserves parking lot will be on your left.
Fun Facts: At one time 25% of Long Island was covered with the richness of the Pine Barrens. Protecting the Pin Barrens afford 3-5 trillion gallons of public drinking water located in the deep recharge aquifers. Hydrologists have estimated that the pine barrens recharge some 175 million gallons of purified water each day to those aquifers.