Here are a couple of bodges from when I was back in school (i.e., over 25 years ago). Sadly, these projects would be more difficult for me today.
TV remote: Before TVs came with a remote control, I wired a long cable to my computer's joystick. Feedback came through speech synthesis (the TV was busy), and when I pressed the button, a servo would select the channel I wanted.
Coin relief map: I wanted to digitize the relief (imprint) on the surface of a coin. I used a pin in a capillary tube with two coils of fine wire to make a variable core transformer to measure z-height. The x-y stage was Lego Technics, with PWM controlled motors (running on an ARM2 in interrupt space). It worked far better than it ought to have.
Normally a technician plugs a test machine into the car's OBD port. The testing machine then asks the ECU to send its emissions data so that they can be compared to the actual emissions. Then a spy satellite operated from Wolfsburg HQ detects the uplink from the vehicle, and deploys nanobots via underground tunnels to clean the emissions.
One of the sentences above is not true, but would make a cool movie.
Personally, I am a bit disappointed that the reward wasn't 256k.
AT&T's rewards are on the "unlimited dollar" plan, and it got throttled.
If you stop watering trees in California, the trees die. We had an orchard near where I work, when they stopped the irrigation, half the trees dried up in the first year. (They're developing the lot, so there was no hope for the orchard anyway. But it was still sad.)
What this country needs is a good five cent ANYTHING!