Mini project idea in electronics?

I would suggest a simple circuit based on a 555 timer IC that will give a delay to the turning off of a cars interior light after you shut the door.

Total cost would be about $10 and aside from the IC you only need a transistor and a few passive components. -- EASY PEEZY.

And before you ask - NO , I am not going to design it for you. :-)

Something trucks have and cars don't usually have, a reversing beeper. The beeper is activated when the reversing lights go on, but not if the tail lights are on so you don't annoy the neighbors at night. You could get cute and use a speech chip to say "Warning, reversing!" instead of a beeper. Built one with a beeper myself years ago.

make a "ineffective gadget". its normally a field with a change and a door. once you turn the change the door opens and something comes out to coach the change returned off. or the single thats basically an electric powered toy automobile which you plug right into a wall so it merely starts off driving and unplugs itself.