On a project with so few parts, every part does a few jobs!

Since I left out a switch of any kind, the best (and only) way to turn off the pin is by disconnecting the battery. Here's where the pinback serves double duty. By holding the battery in place, the pinback forms a rudimentary switch, conveniently allowing the user to slide the battery up and down to turn the pin on and off without having to remove and possibly lose the battery:

The battery itself does double duty as well by reflecting the LED light off its mirror-finish edges, enhancing the glow around the edge of the pumpkin:

Even the LEDs do double duty. Since the CR2032 battery is held in by friction and nothing else, the bottom two LEDs form a physical barrier which ensures the battery cannot slip out the bottom of its holder:

Finally, the entire pin does double duty! By folding the LEDs to point upwards, the pin can quickly be converted to a safe, flame-free jack-o-lantern light!