G. Mark’s Answer
Just about everything. My first car was a '68 Chevy Caprice. I decided to take the engine apart and spread it over the driveway and choose parts to change. I worked in a warranty parts area in a dealership, and those parts that were decided as "defective" and to be discarded, I'd figure a way to make them usable. I put a lot of parts together to get a functioning AC system into my car. At the time, AC was special, and I figured out how to evacuate and charge the system with Freon and it worked.
Today, there's a lot less that's dependably familiar across car models. But the wide variety of technology is also voluminous. That is to say, mostly every car today has more gadgety stuff in it than most office buildings by far. I tell my students that if they want some ideas for innovation, they should visit a junk yard and tear into some cars. There's so much clever stuff in there it's amazing. It used to be that there was so much room in some cars' hoods, that a mechanic could sometimes literally stand in the engine compartment of some vehicles. Today, you could throw a pack of BBs in there and none of them would hit the ground.
Take apart a brake caliper -- you'll see some technology that you simply can't see how it works without studying some articles.
When I got my first Cadillac, I was amazed that the computer had several modes, one of which was to transfer the functionality of other indicators and gauges to that central cluster where the radio was controlled. And it had a menu mechanics could cycle through to display the output of all the sensors in the car. That was over 30 years ago.
I was talking to an astronaut once and I remarked how amazing the engineering on the Shuttle was. He said, "It could be worse. We could have been designing a family car. The Shuttle goes into the vacuum of space and gets really hot. The family car goes through four seasons, gets left outside in the wind, snow and rain, and then they throw road salt at it, and let it sit and get cannibalized by electrolytic corrosion. And then your kids dump soda pop into all the mechanisms. And it still works. And usually, nobody does anything to service it again until it goes to the junkyard."