Traveled to NY one year in my RV to visit an uncle. His neighbor was an Undersheriff who stopped by to meet me and ask me where I stayed when on the road. I told him I pulled into Rest Areas and napped when I was tired. He told me in NY it was illegal to camp in Rest Areas. My response was camping without beer is just sleeping outside and I didn't have any beer in the RV. The next evening he stopped by again, but this time he came with a couple of cold beers that we enjoyed together.
My take-away is if you're using the Rest Area to get some rest, you're OK. No LEO wants to see sleep drivers on the road. If you're picnicking, you should be OK but if you're camping with lawn chairs, slides, BBQ grill, lite strings and flags you're probably not OK.