In the lower price ranges, single use items like firestarters are always appreciated. Packaged side dishes like rice and pasta make good stocking stuffers. Even for those of us who cook a lot from scratch, they are useful when time is short or other resources are scarce (like good weather.)
There are some wonderful books out there (besides the Frannie Shoemaker Mysteries, of course.) A friend recently loaned us Parklands of the Midwest. I think we will need to get our own copy. We never travel without Camping with the Corps of Engineers, a guide to all of the COE campgrounds in the country. And a new atlas never hurts. A truckers' atlas is especially useful for people with large RVs because they note low clearance areas and other useful information.
Of course, flashlights, first aid kits, and weather radios are necessary gear for most campers. We find the cheap foam cushions they sell for boating helpful for hard picnic table benches or even lawn chairs. Solar lights of all types come in handy. And don't forget the bug spray.