it does sound awful I know, but in practice some of the requirements are common sense [well anywhere other than the UK]
Vehicle
1 - all original documents - insurance, licence, registration
2 - warning triangle [or 2 I think in Spain], hi-visibilty vest for driver AND ALL passengers in the event you break down and have to get out of the vehicle for any reason
3 - beam-benders to correct UK extreme left angle on lights, there's only one basic type I think
4 - first aid kit - [compulsory in Germany]
5 - if you need glasses to drive make sure you have spare set
6 - spare set of bulbs [never been sure what you're supposed to do with them though]
check out Halfords or AA, you can buy kit containing all necessary bits - don't know if it costs in because our stuff has been acquired over time. and having got it and thought about the logic of it can't imagine why most of this stuff isn't compulsory in UK
In fact if you check out either AA or RAC website they both list requirements by country and also say whether it's recommended or complusory
also - France is supposed to be bringing in breathalyser requirement later this year, before getting one remember that different countrys have different tolerance levels.
Camping
1 - Calor gas not obtainable outside UK, camping gaz is but is incredibly expensive, first ask yourself how much gas you need and how much you can carry - you're likely to find that you can carry all you need unless you're on a really extended trip. In which there are ways around it
2 - Electricty, you'll need to carry euro two-pin adapter - not all sites have 3 pin points- especially the smaller ones.
3 - also Electricity - hate to start this topic, but there is something called reverse polarity - really really really isn't a big deal, get a short length of standard EHU with the 3-pin connectors at either end, open up one end and reverse the neutral and live leads, put it back together.
your van electrics will probably tell you if you need to use it, if so simply fit the converted lead onto your standard lead and forget about it
Camp sites
1 are generally more relaxed about everything, if no-one in reception, park up anyway, at some stage you'll get around to registering and paying.
2 carry substitute for your passport, aka Camping Carnet International - or the new version supplied by ACSI, . Since they contain your name and address you're saved the embarrassment of having to say more than bonjour when you register
3 - may need to obtain tokens for showers, washing machines - in France they are known as 'jetons' - get them from reception
4 off peak - [in France pretty much anytime outside mid July - mid August]
part of the toilet / sanitation blocks are likely to be locked, saves effort on cleaning, DO NOT BE SURPRISED by unisex showers and loos
not sure if this makes sense, I'm off for a brew and will see what else I can come up with to frighten you
PS speed limits, vary depending on weather conditions, strict 50kmh in towns / villages - starts at the 'name sign' again I think AA / RAC web sites will give details of different rules
PPS are you in either of the 2 main clubs? Caravan Club handbook used to be pretty helpful.
but, don't panic, you'll have a great time