Wild ponies, sandy beaches, crabs and clams, open skies: Assateague is a unique Atlantic destination capturing the best of the sea and wrapping it up in ... camping! That's how I was sold on it, at least. My family of four headed east over the recent holiday weekend. There were three families — 6 adults and 6 kids total across three reserved camp sites.
Getting there & setting up
Our friends left Baltimore Friday afternoon and hit traffic. We left DC before sunrise Saturday morning and did not. While they got to wake up with wild ponies rummaging through their trash (more on them below), we missed setting up a tent in the dark and wind. Sunset is at 6:30! While my wife took the boys to the beach, I set up the tent and put all the sleeping gear into it.
The campground is on a separate road from the rest of the park, which means there's not a lot of traffic. The kids all had scooters (except my infant). Other bigger kids had bikes. Either will allow them to get back and forth to the camp store and playground with ease. The bathrooms (and water and trash) are on every other loop, so one thing I'd add to my next trip is a collapsible beach wagon to wash off toys and gather water. (I bring a 5 gallon water tank for camping trips. 5 gallons = 40 pounds.)
At your camp site
There are no trees in the camp ground area. The paved parking pads are among the dunes. That means no wind breaks and no shade. For your tent, you'll want a mix sand stakes and regular stakes. Regular stakes can go into rooted vegetation without a problem and sand stakes for the, well, sand. Try to set up your tent at a 45 degree angle to the prevailing wind so a corners is taking the brunt of the wind, not a wide wall. You'll also want to weigh down the bottom of your tent with all your sleeping gear. (Nothing with a scent though, see Ponies below.) And then, create cross-ventilation. In addition to keeping your tent grounded, it will keep it cooler in the summer. You can either leave your tent without the fly so it's mesh all around, or if you want to set up the fly (for shade, day naps, so you don't have to do it later), then open the front and back door of the fly if you have it.
Also, there is no shade. (Did I say that already?) Time to use a camp canopy or an EZ-Up. For either, you have the same wind problem as described for the tent, so put it up and take it down as you need it, rather than creating a heavy metal kite!
Finally, a note about the late summer vegetation: on the plus side, there's milk weed, so there are butterflies everything. On the minus, there are less desirable plans that aren't stinging nettles, but like those Appalachian plants, they have small spiky balls when they dry out that will get stuck everywhere. Walk on the paved areas, not through the grass. Will also simplify your tick checks.
Things to do
A lot of people had kayaks, canoes, clam shovels, and fishing poles in addition to the afore-mentioned bikes and scooters. Packing camping *and* beach stuff was enough to fill my car's trunk to the gill, but if you have the sky box or a trailer hitch, you can add tons of variety. My kids only went to the Atlantic beach side, but on the bay side the water is calmer, and the cove up by the visitor center is even more toddler-friendly. If you drive to the end of the state park road and have 4WD (and a rope and a shovel) they'll let you drive on the sand, for a fee of course. You can also "backpack" as far as 15 miles south and find three designated backpacker campsites along the way (reservations required, but almost always available, according to the Ranger). I'd definitely consider a flat top kayak for a bayside cruise next time.
The best way I can describe them is this: pretend they're bears. Beautiful from a distance, but a kick to the face by a wild horse is bad news, and they are not tidy houseguests. If you wouldn't leave it out when camping in Shenandoah or the Smokies, put it in your car at Assateague, too. Anything with a scent! As noted, our friends accidentally left a bag of trash on their picnic table and awoke to a half dozen ponies fighting for it and kicking up sand in their camp site. And leaving other ... evidence ... behind.
While Assateague in the summer can sell out, DC-area summer weather starts before Mother's Day and extends well into October most years. Our off-season trip meant the ice cream stands in town were closed, and lunch at Ocean City on the way out wasn't quite the scene it is in August, but we had the beach to ourselves. Advance reservations are needed but if you need just one site, chances are unless it's a Saturday you can find one.