Hrmmm lots of ways. You could sell ads that tell you about where to eat - Google Now, you could use the glass on the vehicle to project billboards and so forth, or just project ads inside of Google Glass. You could just use it as a way for people to consume more Android apps or read more of the web, both of which make Google money.
The point is, it's all a giant machine to sell more ads in various forms. If you think Google won't sell ads on Google Now or Glass or inside the cars, or whatever, then you are kidding yourself.
