Try on some NeoPixel strip and cut to the size you like. I found that a 1m strip was perfect for my bandolier, but you may need more if you are not a petite lady, or slightly less if you are making a belt.
The 3D printed bullets were designed to line up with 60 pixel-per-meter strip.
Strip and tin three different colored silicone-coated stranded wires.
Solder the wires to the input of your NeoPixel strip, alternating solder joints from the front to the back of the flex PCB to avoid overcrowding.
Solder the other ends of the wires to GEMMA as follows:
GEMMA Vout to NeoPixels 5V
GEMMA D1 to NeoPixels Din
GEMMA GND to NeoPixels GND