Portable DIY Teensy Synth
Chowdah 
Play!
Depending on your USB pack, you may first have to press a button on the side to initialize output. Close the box and flip the main power switch, and the mute button/light will illuminate to tell you that it’s ready to go. From there... just start pushing buttons. The synth is designed to be self-explanatory — no one needs more stress when the world is ending. After a few seconds of banging around, you should have things figured out.
When you’re ready to go into stealth mode, press the speaker mute button to turn off the external sound and plug a set of headphones into the aux jack. With headphones on, you can play for just yourself.
Alternatively, if you want to GO BIG, plug it into an external amplifier and crank it up. Or connect a recording device and save your sessions for later. Apply power to the USB-A port to keep it charged up when you’re done, and you have a portable instrument that’s ready to go today… or even if things get crazy tomorrow!