The law changed in France and Belgium last year (check Germany somebody?) and you now have to have a high-vis vest in your car. It has to be in a place where it can be put on without the need to get out of the car. Its use is mandatory in the event of a breakdown or accident. There is (being France) an on-the-spot fine for non compliance of I think 130€ - similar to not wearing your seat belt. Some policemen see foreigners as an easy target. The vest, like the warning triangle needs to carry a CE approval and you can get fined for not having the right sort. Contrary to what they might tell you in Britain, you only need one vest. Other things to note - don't have a laser detector or jammer in your car, you'll be in very serious trouble if you do. The police carry a file with them telling them exactly which are legal and which aren't, so you can't talk your way out of trouble. Oh yes and you can have your car confiscated for serious speeding in France and Belgium - 120mph plus and you might not get it back. Germany's a whole different ballgame so wait till you get there before nailing it.
Just found this - http://www.theaa.com/motoring_advice/touring_tips/compulsory_equipment.pdf