Valerio Nappi posts about generating true random numbers from bananas:

It was a dreary afternoon in Milan last year when, procrastinating on studying, I was struck by a flash of genius. “What would happen if I made a banana-powered random number generator?“. I immediately went to tell my roommate, who was also an electronic engineer.
He looked me in the face and burst out laughing. At that moment I realized that I had a great project in my hands.

The possible way using bananas is that of radioactive decay. Bananas in fact are known to contain a lot of potassium, and a small but significant percentage of the potassium present in nature is radioactive. Specifically we are talking about the 40K isotope, which makes up 0.01% of potassium in nature. Plus they’re delicious with lemon and sugar, which alone would be a great reason to always have one on hand.

See how Valerio uses a banana and math to make a good true random number generator in the intro post here.