Just pinched this off the Web.
Before you drive in France, ensure that you have a High Visibilty Jacket for the driver and, ideally, for all occupants.
The law came into effect on 1st July 2008 making a requirement for the driver of the car to wear a high-viz upper body garment (waistcoat, jacket, anorak) if the car is immobilised at the side of the road or on a hard shoulder and the driver has to get out of the car. The jackets have to be within reach and inside the car - not in the boot. The jacket should carry the correct CE mark to show that it meets the current legal requirements.
A warning triangle is also obligatory under the same law - this may be kept in the boot though. The purpose of the triangle is that in the event of a breakdown you place it on the carriageway some distance before your vehicle to warn other drivers of the obstruction. When placing hte triangle be mindful of your own safety!
High-viz jackets are not obligatory for passengers, but you are advised to carry in case they, too, have to get out of the car.
When hiring a car, check that a triangle and sufficient jackets (gilets) are provided.