Take your insurance documents, originals not copies of everything.
You can do 1 breathalyser but the advice I've read suggests 2, in case one is faulty or the police ask you to use one - in which case you'd have to go and buy another immediately to remain legal.
They're sold in 2s here anyway.
Hi vis vest needs to be inside the passenger compartment, not in the boot as you're supposed to put it on before you get out in the event of an emergency (makes sense really).
I don't think you actually need bulbs or the extingisher
Compulsory equipment abroad | AA
I got pulled years back on the autoroute - I was doing about 135kph but the traffic cop showed me his speed gun reading 150kph.
The only reason I didn't see the cop was I was being tailgated by one French driver while another forced his way past me on the right then cut across to avoid hitting a truck. I was concentrating on not getting rammed or stuffing the undertaker into the truck that I only clocked the blue focus on the hard shoulder after we'd passed it. My own fault I shouldn't have sped up to try and get out of their way and made them do the work.
The French drivers were clearly racing and I suspect the speed reading was the undertaking car but they kept on at full speed but I pulled in and slowed down to the limit.
Off the autoroute/peage stick rigidly to the limit for the reasons Epicurus mentioned, even though many French drivers will be all over your bumper because of it.
It's also worth noting that if you can't pay an on the spot penalty in cash they're able to impound your car until you can, so make sure you have some Euros in the car when you get off the ferry just in case you get taken by surprise by a speed limit change.
Last time I drove in France they had very prominent warnings about cameras but they've removed all of them and it's not legal to have speed trap detectors or sat nav displays with camera locations visible either.