Warning triangle, spare bulbs, are essential, and a first aid kit is recommended. Additionally it's recommended to take high viz vests (under French law if you're the first to happen on an accident you have to stop to help - and a high viz vest is useful in breakdowns, too). If you wear glasses then you need to take a spare pair, too. We also pack a fire extinguisher - but haven't had to use it in France.
You'll need a Continental plug tail to enable your EHU cable to be plugged in to the power supply.
Polarity Tester
Ample gas supply if you have Calor that can't be exchanged on the continent. May be get a large Camping Gaz bottle and reugulator as back up.
Apart from good map, Satnav with continental mapping to use along with your map or route finder. Apart fron knowing where you are it help when you may not understand signs.
Andrew ,additional to val's post I recommend a reverse polarity connection & a continental type connector for your electrical lead plus a polarity tester to check the site supply. you will have to make your own reverse polarity connector you can get a continental connector from you local caravan/camping store, a reverse polarity/plug tester will be cheaper at an electrical wholesaler & so will the required male/ female connectors for your reverse polarity lead( as fitted on your electrical lead)
The French and the German two pin plugs are not quite the same although they are the same size. The French have a third pin in the socket for the earth connection whereas the German earth connection is by two metal strips at the side of the plug. This makes the German system completely reversible, which the French one only is if you have a flat Euro 2-pin plug without earth. As soon as you need an earth connection, the French system is no longer reversible. A few Continental plugs are designed to accommodate both the French third pin and German earth connection, but generally they are specific and one would need an adapter.
Check your tyres on the van,if they are 13" take TWO spares,we had one disintegrate in the heat,fitted the other which was starting to go the same way and there wasnt a 13" tyre to be had in France,apparently it is an odd size there.It took a week to get one.Be prepared to have a sense of humour and to be ready for "Non" as although the country is lovely the french seem to like the phrase alot where anything that departs from their instruction book is concerned!!!!!!!!!!!!!!!!!