DIY phone charger
Even though my smartphone has quite a long battery life, I still get worried that I might run out of battery while on the go.
So for a holiday trip, I built an emergency charger with some parts I had at home and some that I bought: a 9V rechargable battery, some capacitors and cables. In total, I spent 1 Euro on the project.
I soldered the parts and fixed them into a box with sugru - my new favorite material.