A while ago my son's school entered a competition where they made their own slot cars with vacuum formed plastic bodies. They were allowed to bring them home and 'pimp' them.
So being British we decided to interpret 'pimping' rather conservatively and take it to mean adding headlights and working brake lights.
Here is the schematic:
When there is power on the tracks, the headlights are always on, but the diode will bypass the Brake LEDs and charge the capacitor. When the controller is released and the supply voltage drops to zero or open circuit, then the current flows out of the capacitor lighting the brake LEDs discharging through the stationary motor for a couple of seconds.
We didn't win the race competition, but actually I think the electronics was more fun anyway.