I also enjoyed the GPG talk. Other highlights:

Not an Impasse: Child Safety, Privacy, and Healing Together: https://media.ccc.de/v/39c3-not-an-impasse-child-safety-priv...

APT Down and the mystery of the burning data centers: https://media.ccc.de/v/39c3-apt-down-and-the-mystery-of-the-...

Bluetooth Headphone Jacking: A Key to Your Phone: https://media.ccc.de/v/39c3-bluetooth-headphone-jacking-a-ke...