Decent wine glasses.
Bottle opener, corkscrew.
Warm clothes and blankets.
Spirit level, if our van isn't 100%level, the fridge won't work.
Do you have an awning??
"Beer bucket"
Do you have a cooker? Ours is just a hob, so we have a separate toaster and a slow cooker.
Find a home for everything and put it away as soon as you are done with it.
If your shower is practical to use(Ours is not) have 2 water butts. And always check your water. It runs out quicker than you realise and the pumps burn out in no time, which is an expensive faff to fix!
Have plenty of dry and tinned food in, but try not to buy to.much fresh stuff. We start off with good intentions, but then think sod it and have a pub tea/lunch.
Balance your van contents to make towing easier, this will take a few attempts to get right.
Have a snack/water to hand when you arrive, your DH will need it after towing.....it takes it out of you, especially if he is new to it and you go over an hour away.