Why not „enlighten“ a bag when opening it? This comes in useful especially in the dark.
making it happen
Sew the components in a bag as shown on the pictures. Alternatively test everything using the alligator clips before sewing.
Realize the zipper switch to turn on the Gemma MicroController when the bag is open. A small plate with soldered cables is used to make the connection only when the zipper is open (=switched). Ensure that there is no connection on the plate for the bridged cable! Transparent nail polish helps to keep the knots from undoing. Needs several hours to dry!
the source code
Load this program on the Adafruit Gemma.
how it works
When the zipper switch is used the microcontroller is powered on and turns on the LEDs one by one.
The Gemma and the Neopixels are also available in starter kits.
Of course there is no guarantee this description is free of bugs!