Beam blockers/benders for the lights. The alcohol testers thing is now gone thankfully.
High-vis jackets you can reach without getting out of the car.
Do take your insurance cert for the car - very handy if you get stopped.
Had a Satnav too instead of using data on a mobile for routes and planning. Obvs one that covers Europe and updated as new as it can be (or use a mobile which is clearly easier but MAY cost)
If you DO use a mobile/satnav the French are VERY funny about displaying speed cameras. Systems are NOT allowed to display this detail so worth disabling it if you can and then sticking to indicated limits.
Breakdown cover!! I've just come back from France in my V70 - Well I wasn't IN the V70 and it was on the back of a recovery truck....
I used CBC (a broker) and it was about 80£ for an annual policy including European cover. Worth every penny in the end. Broke down once in France and recovered back and then again in the UK. Car HAD been very reliable and had never broken down/not started before. It's still not fixed and remains on the drive
https://www.comparebreakdowncover.co.uk/