Xenon Strobe Light:
Build a strobe light using a disposable/throw-away/one-time-use camera.
When mounted on an RC airplane, it really looks great, like the real thing. Even in bright sunny day, you can see it clearly from way up high.
Cheap 12V Power Supply:
Modify an old AT/ATX power supply out of an old computer and use as a general bench-top power supply.
Configure it to regulate for 5V or 12V. Use it to power your hotwire foam cutter, or use as the main power source for your LiPo battery chargers.