Every participant of PyCon US 2019 received a CircuitPython Playground Express (cpx) in the swag bag from Digikey and Adafuit, which is one of the best swag in a conference. Only another thing which comes in my mind was Yubikeys sponsored by Yubico in a rootconf a few years ago.
The goal is to guess a color for the next NeoPixel on the board and then press Button A to see if you guessed right or not. Py and I are continuously playing this for the last weeks.
The idea of CircuitPython, where we can connect the device to a computer and start editing code and see the changes live, is super fantastic and straightforward. It takes almost no time to start working on these, the documentation is also unambiguous and with many examples. Py (our 4 years old daughter) is so excited that now she wants to learn programming so that she can build her things with this board).