We're planning a late September bike trip. Will food trucks still be on site and are other facilities and food services open?

There are restaurants and food venues within a 1/2 mile of the park's entrance.

Most likely on weekends, summer does not end until September 22, that would be late sept.

I doubt it, after first week in September no food trucks. Call to make sure.

Bathrooms will be open, but you should definitely bring in your own food and drinks.

I would call the national park service at sandy hook. I believe after labor day everything shuts down