Offer a pull-down center armrest with cup-holders. Might also have some additional storage.
Common in many cars with stationary rear seats, but not often found with seats that fold down like the Model S. When equipped, it is usually a standard feature. This feature (when up) usually makes the center seat position more uncomfortable due to less padding.
The Model 3 and Y both have this feature from the start. The 2021 Model S includes this feature without additional cost.