Autonomous cars offer passengers a rich platform for Augmented Reality entertainment, with complex sensing that can drive passenger experiences by tracking, appropriating and altering elements of reality. This paper forms an early exploration of in-car AR games, starting with how existing game genres might work within an AR vehicle context, appropriating elements of reality (e.g. other cars) into gameplay, and altering the appearance of reality in relation to game events (e.g. augmented cracks in car windows). We discuss results from focus groups exploring an initial AR game prototype, and an informal in-car evaluation of a follow-up prototype inspired by the focus groups. Broadly, we found that participants enjoyed using AR gaming in-car, noted the immersive impact of appropriating real-world elements into gameplay, and felt that it improved their experience of the journey. We reflect on the ways in which future AR passenger experiences might take advantage of the available sensing and environment to create engaging reality-based gameplay.