Yes to audiobooks - both in car for all to listen to and on iPods/phones with headphones for individuals. Ours have tablets each too, plus books and puzzle books. They are 9 and 11 though so largely amuse themselves.
We don't bother with the toll thingy, but we never drive on main transfer day (saturday) so that probably helps. We normally break the drive overnight.
Aires, as others have said, can be dodgy toilet wise, we stop in proper services if at all possible.
You don't need the breathalysers; technically the law requires you to do so, but the fine for not carrying these was "postponed indefinitely" a while ago, so there is no penalty for not doing so. (The limits for drink driving are very very low in France though so don't!)
You do legally need a warning triangle, and a reflective jacket (kept in the passenger compartment not the boot). You are supposed to carry your V5 as well.
Headlights need to adjusted to avoid dazzling oncoming drivers so get some of the headlamp stickers converters. You also need a GB sticker unless your registration plate already displays one.
Its prohibited to carry any device capable of detecting speed cameras; many sat navs can do this so it's advisable to switch that capability off in case of spot checks. Though if you are driving sensibly it's unlikely you'll get stopped. Many cameras are unsigned so be careful and obey speed limits! It's also now illegal for a car driver to use any in or over ear equipment (like bluetooth phone headsets).
Driving on the right is relatively simple, just keep an eye out for "priorite a droite" - priority to the right - which still prevails occasionally at roundabouts, and means that some (usually older and more used to the convention) drivers will pull out onto main roads expecting oncoming traffic to give them priority!