I live in Philly and have done two cross-state tours to home.
The first was from Pittsburgh via the GAP trail to Cumberland, MD then mostly U.S. 220 to Bedford, PA where I picked up PA Bike Route S. Took that all the way to Lancaster County where I modified the route to get me home in a nicer fashion. I also cut out a big climb out of Betzwood, PA by riding the section of the abandoned PA Turnpike, which is an unofficial bike trail and was used as one of the filming locations for the film "The Road" starring Viggo Mortensen. . I highly recommend it as long as you have a good light and are not afraid of the dark. There are two long tunnels (the longer being over 1 mile) with no lights. The second tunnel heading east has a crown closer to the east portal, which means for much of the distance you literally cannot see the light at the end of the tunnel. The nice thing is that you can still see the median striping inside the tunnels so you can use that as a guide.
The second trip started from the Youngstown-Warren Regional Airport near Vienna, OH. Made my own, nice route to Franklin, PA where I picked up the scenic, paved (except for maybe 3/4 of a mile) Allegheny River Trail for about 25 miles to Emlenton, PA. From there, I followed PA Bike Route V all the way to Rupert/Bloomsburg and then headed south via my own route, which included the abandoned town of Centralia. Depending where you might want to go in NJ, you could stay on Bike Route V all the way to the end at Portland, PA and cross the river there into Columbia, NJ via the pedestrian/bike bridge.
Overall, the PA portion of the latter trip was nicer (and more challenging) than the former. Both routes had pretty well-spaced camping (There is free, trail-side camping with Adirondack shelters in Franklin, PA, right along the river. Saw two bald eagles in the morning.) and access to good grocery sources along the way, although in many instances I hard to carry groceries for some miles as there were no stores close to my camping locations. Let me know if you would like detail on one or both of the routes.