Hi and Welcome! Unfortunately, last minute reservations during holiday weekends on Long Island are tough. You could call Indian Island County Park, Wildwood State Park, Smith's Point County Park, Cupsogue County Park, Cedar Point County Park or Hither Hills State Park to see if there are any cancellations. Check the websites for the State and County Parks. Get a Green Key card at any county park or golf course so you can reserve sites. Sign up with Reserve America to reserve sites at NYS parks. There is a tiny CG in Cutchogue called Cliff and Ed's campground. It is expensive, but quiet and immaculate. Google that to find the number. Eastern CG in Greenport is packed because they cut all the campsites in half some years ago. Good Luck and Happy Camping!