Generally VALID ID is required, your permit is no longer valid once it has expired. Some places might take it, and it may go through all the checks w/o a red flag, but then it might not.
My advice is to A) go get your license, B) renew your permit if possible, C) get an ID card (like a license but wont allow you to drive), or D) buy your gun on the last day that your permit is valid (I assume that is your 18th b-day).
Better to deal with it that way then risk a red flag on a background check in a state like NJ.
Edit: Sorry, read NC though NJ...still the less hassle the better
Good Luck