You will need:
- a spare set of bulbs (Halfords sell these)
- a Crit Air sticker (most regions/cities seem to want this now, so definitely worth getting - costs around €5, and you apply online
- a high viz jacket for every person in the car
- your insurance documents
- your driving licence(s)
- your V5
- 'beam benders' if you're going to need to drive with your headlights on
The RAC/AA websites will also tell you if there's anything else that you need, but I think that's the full list
We've just come back from a couple of days, so it's fresh on my mind!
In general, driving in France is pretty easy. Their main roads usually avoid you having to go through town/city centres.
If you do find yourself in a town/city and not knowing which way to go, look out for signs that say 'toutes directions' and they will guide you out of the town/city.
Beware that there are different speed limits when weather conditions aren't good - especially if it's raining, and French traffic police are strict. If you get pulled over and fined, they will escort you to the nearest cash point for the money! (So probably also always worth having Euros to hand!)
A lot of their main roads/motorways are 'péage' - tolls - so be ready for those. As PP have said, you can buy tickets in advance, although we've never bothered to do that. Many of them are automated these days, and take cards - just check the lights above each lane, to see if it's card or cash.