For collector guns, there are two expressions used, "NIB" or "new in the box", which means that the gun is in its original box, with all normal accessories/papers, and has never been fired. "LNIB" is "like new in the box", meaning that the gun is in its original box, and may have been fired or handled, but shows no noticeable wear or handling marks. There are many refinished "NIB" guns with fake boxes (especially U.S. Model 1911A1 pistols), but if genuine, the box can add 10%-50% to the value of the gun.
Ordinary guns are usually just described as "with box", and the premium is seldom more than 5%-10% if that. I do suggest that unless storage space is at a premium, the purchaser of a new gun should keep the box, along with cleaning rod, manual, warranty card (if you don't send it in), test target, and any other material in the box. It does add value later on.
Jim