For driving in France a GB sticker is compulsory unless you have the GB Euro symbol on your plates - which it looks like you do looking at your avatar.
A green card is no longer compulsory, although some insurers will still issue one. You need to make sure your insurance company knows you are going to France, and that you will be insured fully comprehensively. A lot of insurance policies only cover you 3rd party unless you inform the ins co before you go and pay an additional premium.
I believe a warning triangle, spare bulbs and first aid kit are 'recommended' but not compulsory - for Le Mans I always take them just to keep the Gendarmes happy. A lot of drivers also keep a High Visibility waistcoat in the boot in case they have to get out of the car on the autoroute.
There is an official list from the AA...
http://www.theaa.com/motoring_advice/overseas/compulsory_equipment.html
DO NOT take your radar detector (not even unplugged and hidden in the glovebox). They are forbidden in France and if the police have the slightest hint you have one in the car, they will make you empty the contents of your car at the side of the road, then confiscate the detector and fine you heavily (on the spot fine). I've heard stories of the police making you drive over the detector with your wheel - but might just be an urban myth.
Also, look out for radar traps - especially nearer Calais. The french government has had a crackdown in recent years on speeders (esp British Registered cars). Look for dark blue Peugeots and Citroens tucked in between the autoroute and the onslip, and also on the onslip after service areas.
Best advice of all - have fun and make sure you get plenty of good wine!
Editted to say I was writing this as Snarf was writing his reply! [
]