Bellplain State Forest near Woodbine, NJ has camping and, I believe, some trails you can ride your MTB on. (Albeit flat.) There are some guys who have a good roadside BBQ in Woodbine during summer weekends. It's called Kingfish. It's on the "main drag" in next to an antique store.
You don't say whether you want to tour with the bike or drive somewhere, camp and do day rides. If the latter, you could ride up the Lehigh Gorge trail from Jim Thorpe, PA to Whitehaven then take roads to get to Hickory Run State Park. Even if you car camp, there is a lot of MTBing in the Jim Thorpe area. You can get trail maps from Blue Mountain Sports in town.
Bull's Island in nice. Reservations a very good idea for the weekends. Also in Hunterdon County are Spruce Run and Round Valley. Both are state parks/recreation areas. The problem with the latter is that the campsites are all wilderness sites. You can only get there via foot or boat. I know someone who pushed the bike to get to a campsite, but that doesn't sound like much fun. Another trail that comes to mind is the Columbia Trail from Highbridge, NJ north to Califon. (Eat at Rambo's General Store.) It continues into Morris County for a while under a different name. Despite being influenced by development along the I-78 corridor, Hunterdon County is still a beautiful place to ride. So is Warren County to the north.
If you really want to range, you could get yourself to Trenton, ride the D&R to Bull's Island, then continue north on the NJ side to Belvidere, cross into PA, continue to Delaware Water Gap, PA then cross back over into NJ to get to Worthington State Forest. From there, ride through the Delaware Water Gap Nat'l Recreation Area then on to Pt. Jervis, NY, where you could use trains to get back to Trenton.