As per others, I've never bothered with any of the supposed requirements, just the stuff I want to use (i.e. high viz and triangle).
The breathalyser (when I did used to think they were required) and the light kit, I never have bothered, because I figure if asked then the police could never prove me wrong if I said "As it happens I used both this morning officer, just on my way to Carrefour now to buy new ones".
I actually got pulled for a violation four years ago in France, having got sick of waiting at a busy in-town junction I blasted out into the path of traffic. A Gendamerie instantly appeared out of nowhere on a motorbike. Gulp! My first thought was here's a fine coming up, instead he appeared to clock we were English, his English was very poor, so I just got a 10 second 'educational' message that in France this is not legal (yeah, it isn't in England mate) and then waved on our way.
No checking of anything in the car.
I have also been done for speeding in Poland (I'm not proud of these things by the way) and had to pay a cash fine to the officer. He did check my passport (he had a Russian in his car who he had arrested for not carrying his paasport) but again he had zero interest in checking the contents of my vehicle.
I'm not saying they never would check, but you'd have to p!ss them off with some attitude to have them start probing about. They're too busy in reality.
I'm currently 500 miles into France and got no spare bulbs etc, and one week into being in France and covering a good 1000 miles since Calais I have seen one Gendamerie and one traffic cop (virtually asleep at a service station).
In that time I must have seen 50 British cars who don't have either GB on their licence plate, not a UK or GB badge slapped on the boot (which funnily enough, as a visible item I do have one f these). Not seen one person pulled over.
In that time I've also sat on a minibus on a daytrip that consistently drove at 70kph through 50kph village limits, and easily 60kph through 30kph limits. Just to put things in perspective, what British people do or don't have in their cars pales into significance in comparising to everything else happening throughout the country all day!
I honestly wouldn't waste your money on anything, nor spend and furthet timr worrying about any of this, as the cops aren't! Show this to the missus if she isn't convinced.
As with most of Europe, times are tight, outside of the major cities you simply don't see police driving around anywhere, there aren't enough to do so.