Practically, you should be OK as long as it's not a gravity knife, switchblade knife, dagger, dirk, stiletto, billy, blackjack, metal knuckle, sandclub, slingshot, cestus or similar leather band studded with metal filings or razor blades imbedded in wood, ballistic knife. NJ does not have blade length restrictions on knives.
However, NJ has this overly broad law that makes basically anything an unlawful weapon. NJS 2C:39-5 Unlawful possession of weapons.... d. Other weapons. Any person who knowingly has in his possession any other weapon under circumstances not manifestly appropriate for such lawful uses as it may have is guilty of a crime of the fourth degree.
I think they would consider a knife in your car or luggage as constructive possession. So the key is to tell the police that the knife is for a lawful purpose like fishing and NOT for self defense. You're visiting NJ and going surfcasting at the shore. Or you use it to open boxes at work.
NJ is ruled by progressives. If your a shit bag criminal, they are lenient; if you're a tax paying citizen, they'll go out of their way to make an example of you. It's not a coincidence that the NJ State Police uniform resembles a Nazi SS officers uniform.
For self defense, I personally carry pepper spray and a metal pen. It's pathetic but better than nothing. Less than 3/4 oz pepper spray is legal in NJ. I don't carry a tactical pen but a regular Zebra metal pen from Staples. You can stab them in the eye, ear, or jugular/carotid. I think it would be hard to prosecute someone for possessing a regular pen.