An electric continental adaptor if you are not wild camping. A solar panel if you are wild camping and a good supply of reading books to relax with your glasses of wine.
Leave behind the BIG B-bq but take an alternative source of cooking like a portable one ring gas burner or throw away b-b-q. We used to take our big cadac but it needs a big sink to wash that.
A good european road map with relevant dictionary for each country. A good camera/video to record your happy memories. In France you will want the "aire de camping car book" and the caravan club "camping sites in Europe" book as this is the best reference you can get.
Plenty of good tea-bags if you like a good cuppa as they are not readily available.
Depends if you are wild camping or booking ahead. We wild camp and tend to go for the less commercial areas so our needs may be different to others.
Everyones needs are different though. Definitely take all your relevant medicines as we have been caught out with ailments every time. We ran out of our favorite "crunchy nut cornflakes" after 5 weeks touring. No real problem but my husband pouted!
For the van you must have florescent jackets in France to wear if you get out of the van on major roads. A spare set of bulbs is necessary together with a warning triangle and first aid kit. You must also have a spare pair of reading glasses too. Don't forget the E11, driving licence, camping carnet card and passport.
The list is endless so others will add on here when I finish. Enjoy your travels. Wish I was going too but have to wait for next summer now