"How do you know what to provide? I know about autonomous learning, but the parent still needs to provide books, materials, learning opportunities, don't they?"
My daughter is only 11 and not working toward exams, so the above is the only part of your question I feel able to answer. In the case of autonomous education, sometimes the parent offers suggestions and waits to see what the response is.
For example, I download programmes from BBC iPlayer which I think may interest my daughter. She chooses from these and from other programmes that she has found in other ways. I order books from the library which people have recommended in subjects that I think she'd like, or which she has previously shown an interest in. She doesn't always read them - sometimes one look at the cover is enough to decide she doesn't want it. She chooses her own books off the shelf too. She's very keen on sport at the moment, so every time I see an opportunity to try a new sport (if it's convenient for me) I ask if she wants to have a go. I offer various museums, trips and lectures.
Of course what I offer is going to be somewhat biased towards things I like. But that's OK, that's in the natural course of things. Nobody gets exposed to everything anyway. Children whose parents are musicians and chess players will see those activities in their early years and others will not. Children of bilingual parents will have more exposure to languages than other children.
I do also try to provide my daughter with things she says she likes, even if I don't enjoy it myself. Friends and relatives are useful here! My daughter likes opera and is going with a friend next month, which is brilliant because I certainly don't want to sit through it!! She'll ask for what she wants.
There's a fair bit of serendipity too. She'll see something on TV, or there will be a poster up in the library for an activity, or a friend will ask if she wants to do a martial arts session or a science project.
Some parents do more in the way of offering things up than I do, and some do less, leaving the child to discover opportunities and request things that take her fancy. There is something to be said for letting the child take the initiative. Whether compulsory or not, learning doesn't always have to be served up on a plate.