Car-assisted camping I assume (not trekking it all in on your back)? This is a list of everything I can think of that I've taken camping in the past or wished I had with me...
Comfort: camp chairs, sleep mats or air mattresses, camp table, pillows, camping lantern...
Warmth: lots of layers (clothes), silver foil emergency blankets to put on the ground, fire starting stuff, beanies etc (depends on the time of year and likely night temp obviously)
Entertainment: cards, travel board games, books, etc etc, whatever you fancy
Cooking: pots, cutlery, plates, washing up stuff incl plastic tub, salt / pepper, tea or coffee making stuff (helps if this is all together in one container), tea towel, replacement gas canisters for cooker...
Other stuff: ways of keeping everything neat when you don't have drawers/cupboards- think Tupperware containers and ziplock bags; first aid kit; torches; padlock if leaving tent during the day...
Hygiene: loo roll (depends on the campsite, some provide it most don't); kit to take to shower, neatly packaged incl soap, towel, shampoo, toothbrush, toothpaste etc- easiest if you get quick dry towels and keep it all in one bag per person, also flip flops for manky public shower