I love that the national park service uses the term "backcountry camping" It's a phrase I may adapt more and more. On Fire Island you are able to camp out in the dunes (not between March and early Sept when it is Piping Plover breeding season) or the beach. Except for the cost of the ferry to Watch Hill, it is free. There are only 24 slots available though, so on busy weekends in summer they fill up fast. No pre-registering, it is first come first serve only. A link to the Fire Island National Seashore is below.
Fire Island
While we only hiked out about a mile or so, we were forced to carry 5 liters of water, since no potable water was on site. But hind site perhaps you set up camp and then hike back out the one or two miles and retrieve the water separate. Carrying around 35 pounds even for a little while was the most grueling part of the adventure.
Since there are four separate ecosystems in a very narrow space, the abundance of wildlife is amazing and easy to see. For the first time I think I saw almost every creature featured on the Fire Island brochure we were given. There is the salt water marshes on the bay side of  the island. There I saw a Great Egret, Mute Swans, an American Bittern, Cormorants, and I believe American Black Duck. Deer were everywhere, while walking to Davis Park on the boardwalk they ran out in front of use like squirrels. In the dunes area I spied a little fox on three occasions, twice running along the shoreline looking through clumps of seaweed searching for food. In the morning I saw a Harrier (or it could have been a Merlin, not sure) harassing and chasing a murder of crows. Eventually once the brave one had cleared the area of his enemy he took to hunting smaller birds near the marshes. Well off in the distance, there was a very large raptor with white underneath and black above, but I only saw him for a second. I think it was an Osprey. Of the smaller birds, I spent part of my time chattering with a Grey Catbird who was hanging out near some Mockingbirds and I got a bit confused if one species was mimicking the other at times. I brought out my Iphone app Audubon's Field Guide to the Mid-Atlantic and found several Catbird calls which I played. I believe I freaked out my little friend who kept coming closer to check out who was making these weird calls. Also in attendance was a very fancy Rose Breasted Grosbeak, a Northern Flicker and a yellow streaked variety of Warbler, which I really can't identify. On the beach their was a party of gulls, mechanical little Sanderlings and dive-bombing Terns. It was quite the spectacle of nature and am eager to come again when the only creature I wasn't eager to meet has finally left, the mosquito.
Here are some bird calls from the species I saw. Cornell University website has some really comprehensive information on Ornithology.
Northern Flicker
American Bittern
Rose Breasted Grosbeak