Briefly, in France obey the speed limit and no speed camera detectors, license (both parts), insurance cert, mot (if applicable), V5 log book, passport, headlight deflectors, fluorescent jacket for each occupant (inside the car not in the boot), warning triangle, first aid kit, spare bulb kit, fire extinguisher, foot pump or compressor, legal spare tyre, GB sticker or GB badge on the numberplate is acceptable.
Not all required, but all are possibly gonna save you in an emergency.
Full Euro breakdown assistance (can be had for a year online for £59) will get you home or recovered to a garage if necessary.
Have fun.