The closest thing I know of to boondocking in New York City (which, of course, is far from all there is to New York) is Floyd Bennet Field, run by the National Park Service. The tent sites look a lot more inviting than the RV sites, which are just designated slots in a parking lot (albeit one that's somewhat removed from the city traffic). RVs, I think all motor vehicles, are not permitted to be on those the tent sites, though.
I should really say the closest thing other than Gary's post's video that I just watched.