Printed Insurance forms / Vigipirate / idiots
Your insurance company will give you pro-forma insurance claim forms which must be filled out at the site of an accident. These should be carried in the car, together with your V5 and your insurance document and you Drivers licence.
As has been discussed, spare bulbs are not a legal requirement BUT if stopped with a light out, you will not be allowed to proceed.
You need as many high viz jackets as passengers. I have one pukka excellent quality ex-police jacket (price £10 from eBay) and a cycling jacket (it does the job)
The breathalyser thing is a bit of a red herring. It's not really enforced.
Be aware that the police pull cars over at roadside stops, typically near roundabouts. They're looking for coffee coloured chaps answering to the name of Mohammed. (Sorry if that sounds racist, but they're being racist.) It's all part of France's 20 year "state of emergency" called Vigipirate, an overtime creation scheme for tubby policemen. You won't see many traffic cops patrolling in cars.
The most important advice is to be aware that the French drive like idiots and are especially fond of overtaking on blind bends, usually in underpowered Citroens and Peugeots. So expect idiots to create a collision, and take avoiding action. To put some numbers on it, something like 4,000 people die unnecessarily on French roads every year. Eighty a week. But what can you do?