I added a custom control panel for my carputer/carpc in the place where my cup holders used to be:
A picture:
closer:
- Space Navigator (for things like scrolling lists, selecting different centrafuse modules)
- Arcade-style buttons hooked to an Ultimarc mini-pac (for play/pause and triggering voice recognition)
- 16x2 LCD (shows obdii data and other random things, custom code in-work)
- All of this compliments the original touchscreen-based system
A picture:

closer:
