The crucial bit is the choice of the tent.

As already stated you need to decide what kind of camping you want to do, and how much space you have to carry stuff.

You also need to decide how long you are going to stop in one place.

If you want to rush into the bush, or stop at DOC sites for one night, you need to be minimalist and concentrate on a tent which is quick to set up and take down and packs down small.

If you + wife + kids fill the car up then you have to make sure that all you need will fit in the boot - or buy a roof rack (unless you have or can borrow a trailer).

If you want to spend the main holiday at one nice site with loads of other kids for company and play facilities, kitchen, showers etc. then the most important thing is a robust tent with plenty of space.

There is nothing worse than being crammed into a small tent during bad weather with a bored family.

We are spending 4 months camping as we travel round NZ so we have gone for comfort rather than minimalism.

We have a big canvas tent - two rooms plus a shaded area out front as big as one of the rooms - and the head height throughout most of the tent is well above 6 feet which makes a lot of difference if you are spending a load of time in the tent.

We fill our Toyota Camry up to the level of the back seat rests, but then we have two large cases with all our worldly goods to fit in and these take up most of the boot. Without them we would probavbly be able to get most of the stuff in the boot.

You should be able to get away with just buying a tent and air beds if your home is well equiped. Virtually ecerything that we have would be found in our home (but of course carrying it round the world on aircraft is not an option).

Duvets work fine on air beds - one under you, one on top - so if you already have those you don't need to buy them.

Most people have a torch at home, plates, cooking utensils etc.
Camp tables and camp chairs are a good buy (if you don't already have some).
A cooker is fine, but not essential if you are happy to cook in the communal kitchen.
We have two single burner stoves which come in plastic cases and use small cartridges.
Cool box is essential, plus the freezer blocks to keep it cool, assuming you will be near a freezer.
If not, one of the fisherman style which take ice and have a drain at the bottom would probably be better.
A 12V/240V cool box fridge would be luxury (we have one at home and I miss it) but it costs more than a chilly bin.
If you want true comfort, buy a power lead with built in circuit breaker and then all the electric things you have at home can come with you.
Apart from lights and power for the PC and mobile phones, we also have a fan heater which is very nice when the evening temprerature drops into single figures. The electric kettle is also good.

So - enough of this rambling.
If you want to be highly mobile spend your money on specialist gear - lightweight tent, camping stove, pots and pans, sleeping bags, waterproofs etc.

If you want to stay on a site with good facilities for an extended period then spend your money on a big (I say BIG) tent which you can treat as a temporary home and you will probably find that all the things you already have (clothes, cooking, bedding, waterproofs etc.) will do fine.

We started out looking at tents for $200 and ended up buying a tent in the sales (last year's model listed at $2,500 new) for $1,500.
So far this seems to be working very well.
The main gain over small tents (apart from being able to sit inside in a chair and stand up inside) is the large covered area outside.

Hope this helps.
LGC