As for keys, my wife always keeps her key to the A3 in her hand-bag. In the past with a much older Audi I have been in the situation where I lost my key whilst we were a long way from home. No problem, Jenny had her key in her bag. It just depends how organised a person you are. We always take both keys whenever we go out. Several of our friends do the same, so I'm certainly not the only one.
If you don't want to know all there is to know about you car then don't bother to read the manuals. If you car is important to you and like me you want to know all about it, then the manual is the place to go. Some people spent every evening watching television. Personally I cannot think of anything worse. As I said, each to his own.