Phoning in case of emergency 15 (SAMU), 18 (Pompiers), 17 (Police). 112 which you should be able to call from any mobile, even one without a valid sim card, or without credit will get the emergency services. You should be able to get English speaking assistance reasonably easily.
High vis clothing is easily available and widely worn. The cycling club I am a member of gave all members a high vis gilet soon after the legislation came out. Since they are rather good as gilets as well as since French clubs start very early in the morning they are widely worn. While there is no requirement for helmets, club riders wear them almost universally, and many randonées and sportives insist on them. There is no real resistance among the riders for either.
There is a French legal requirement that the public should assist anyone who has been injured or is in danger, and it can be the case that one can be prosecuted for not doing so. I don't think that very much is required other than staying around and notifying authorities, but it would mean one shouldn't ignore anything like this on the grounds that it is nothing to do with you.
If you are involved in an accident either on a bike or in a car with another vehicle you will need to give details in the insurance claims form which motorists should carry. If you are touring and carrying kitchen sinks anyway it may be an idea to carry a couple of these. French law generally, and the insurance firms specifically are less tolerant of the claim that the cyclist wasn't seen, or wasn't injured.