Single air beds (we had camp beds for ours when they were small instead but single beds for me and husband). Picnic mats under the air beds help keep cold out, cushioned mattress protectors also help with insulation and are easy to put on air beds, you can use them instead of sheets if you want to save a little space.
A big enough kettle, and lidded/insulated tea mugs. Proper cutlery. Blankets are better than sleeping bags because you can kick them off when the tent gets hot in the early morning. Separate bath bags so you're not waiting around for each other outside the campsite washrooms. Bug spray/bite cream (essential). Tick tweezers.
If you're camping in the uk, find a local supermarket that will deliver your groceries to the campsite so you're not driving for hours with food in the car. And remember you can always pop in to a local supermarket or hardware store for forgotten things like tin openers or extra blankets, so don't let yourself get too stressed over the packing before you leave, just make a checklist and tick things off and tell yourself you'll buy anything else.
A camping toilet is useful unless you're camping within easy reach of campsite toilets. Bath mats make good absorbent door mats for tents if it's wet.
Also if you're camping somewhere where you don't need to drive, like right next to a beach, remember to run the car from time to time so the battery isn't flat when you're ready to leave, that can ruin the end of a holiday. And I find a small dustpan and brush makes all the difference when cleaning the tent to repack.
Oh, and a groundsheet tucked over everything in the car. That way you can take it out first and unpack the car onto it so the things put in on top aren't sitting on the grass while you put the tent up. It also stops things falling out the moment you open the door, if you're like me and pack the car to the gills and beyond.