Carrying bikes by car in France - what's the real position on stap-ons?

For the cycling part you will need to carry a hi viz vest in case of poor visability. The standard vest workmen use here with two verticle and two horizontal stripes has the right BS# Also bike has to have both rear and front reflectors. The gendarmes tend to be a bit stricter on this than the Brit Police.

Could you get ones for the roof bars, if you have them, as they might possibly be cheaper than a tow hitch one? It would also negate the lights, vision and overhang issues of driving in Europe. Just a height thing for ferry or train so tell them.
Definitely check up with what you need to carry the AA or RAC sites should tell you.

Warning triangle, it was two in Spain before?

Breathalyser, in France

Hi-Viz tabards for every occupant, there are minimums on reflective areas so check if they meet them.

Spare bulbs are not a bad idea, requirements in certain countries as are a First Aid kit and Fire extinguisher.

The best position for using 'strap-ons'?!

Think you may be on the wrong site, but I can't help you out on that one I'm afraid!

And a breathalyser test, warning triangle .........

not sure, but I do know you have to have safety stuff in the boot, hi vis clothing, etc, make sure you check that out

With such a large car, and the threat of theft off the back of the car in France, why not put the inside using something like this?

http://www.hubachercycles.ch/gripsrack/

Well my brother and I traveled from s Wales down to Alpe d'huez last year then to Paris with no numberplate showing or an electrics board and not a single gendarme batted an eyelid ....or a UK copper ...go figure