I've just checked with my French friend, and he confirms what I said, you only need a yellow vest if you actually get out of the car, and although there's still a theoretical requirement for breathalisers, it's never been enforced, even for those Enemies of The State, post Brexit UK drivers. The original law promised an €11 fine for not having them, but no-one has ever been fined, and they changed their minds and have scrubbed any threat of a fine or other penalty. So, Gallic logic. You must carry the things, but nothing will happen to you if you don't, vive la France!

I understood that the requirements in Austria on this are the same as in France, high viz is compulsory if you leave your car, but I don't think anyone who stays in the car has to have one. What you must carry in the car though is a first aid kit, same in Germany, and if you buy a Mercedes, you'll find one of those in a special compartment in the boot.