There's no need to go out and spend a fortune on camping equipment if you've got the van, and in fact although I've been camping under canvas for a couple of decades and have more stuff than you could shake a stick at, I rarely use any of it now I'm in the van. Using general household equipment is cheaper but generally better quality too.
A few things for the list (or things I usually forget!)
- Check you've got gas, there's nothing worse than getting to site after a long drive and not being able to have a cuppa. If all else fails, beer will just have to do.
- Matches or a lighter to light the gas, something I
always forget
- Kettle, frying pan, small pan with utensils and cutlery. Bottle opener
of course
- Warm covers. Whether you're using a sleeping bag or duvet, it's worth taking a spare extra blanket in case of the odd chilly night. I also have a very fetching fur hat I wear when it's really cold in the night (sexy...not!), there's nothing worse than shivering at dawn.
- a battery powered lamp or torch in case your leisure battery's charge gives up the ghost.
- camping chairs, you won't want to sit in the van if it's 'scorccio' outside (yeah right)
- jump leads (just in case)
- a mat or groundsheet outside the van. Especially useful if it's muddy outside
- I've got van OCD and it drives me up the wall when the kids march through the van covered in mud and grass. We usually take some short wellies that can be easily slipped on and off when we're hanging around the van.
- 12V phone charger. Just because.
There was a good thread on here last year with a lot of essential items, if you do a search you may be able to resurrect it (it had a lot of tips about what to stock your cupboards with etc).
Enjoy your maiden voyage, I keep falling in and out of love with my van depending on how badly it's behaving, but all it takes is a night out in the middle of a field somewhere and it all comes flooding back

- I'm sure you'll have a fab time.
Silky