Q2: It varies with period. The rear rack / mudguard mounted ones for a while post WW2 were aluminium in general.
Personally I think they were as much useful as a "throwing in something else" marketing thing. The French tended to go for this rather than cute little saddle bags like in the UK. Period wise a French saddle with a little saddle bag is something I don't have a knowledge, but I know Mafac did a specific (half useless?) kit.
There was certainly enough in those two rear subminiaturis for essential road side repairs and enough to cut up a dried sausage, slap some cheese in a baguette and open a bottle of Beaujolais and stash a crumpled up Michelin map. They would have been stuffed with the only friend to man-kind too ..... an oily rag, To help with all sorts especially for rear wheel removal and keep hands clean.