You must have your passport, driving licence, insurance and car V5. You must also have spare light bulbs for car and caravan, warning triangle, hi-vis jackets (inside the car not in the boot), first aid kit and fire extinguisher. Get yourself the new European Health Insurance Card which replaced the old E111 form.
I also find it good to have enough French to be polite and a phrase book, a good idea of where I'm going, GPS with the right maps in, large scale maps (Michelin orange range). Cash and credit cards.
It's also a good idea to have European breakdown cover.
Hope you have a great trip.
Mark