If you have a toddler, remember a potty. Useful not just for toddler in the middle of the night.
Think about the kitchen stuff you use every day: at least one pot and pan, tin opener, peeler, corkscrew, sieve, sharp knives, chopping board. Plastic glasses are nice.
Wine definitely.
If you don't have a coolbox and ice packs, then think about what you plan to eat in advance and make sure you've thought it through properly: butter no use if the sun is hot (ditto chocolate, disappointingly), but oil OK, and biscuits, and so on. Lots of prepped foods that you might not otherwise buy are useful here: for instance, microwavable pouches of rice can be stir-fried with some eggs and bits and pieces of tinned veg, to make egg-fried rice, and served with soy sauce. Bring basic salt, pepper, sauces and condiments with you. Stock up on UHT milk (bottles rather than cartons are better as you can close them) and bottled water for cooking and drinking (so not just one enormous bottle that you will soak yourself with when you take a swig in the middle of the night).
Also, socks - I read on here that once your feet cool down after the sun sets they will never warm up again, so when it gets dark take pre-emptive action and cover up.
Lots of plastic bags to use as rubbish bags. (NB Don't leave these open near the tent as they attract wasps. Also don't leave food out as it attracts armies of ants.)
Books for when DC are in bed.
Umbrellas, closed shoes and macs so you can escape the tent if it's raining.
Did I say wine?
In-car phone charger essential. Also some of the DCs favourite books and indoor activities eg colouring if the weather isn't what you'd like it to be.
Also wine. And probably some juice boxes / cereal bars / fruit pouches for the DCs to have for breakfast while you come round, plus any particular cups they normally use.
Enjoy!