Plastic pumpkins are a mainstay around Halloween, but if you want to give the ubiquitous little candy holder a bit more character, Adafruit has a guide for adding lights and custom sounds.
Using an Arduino, you'll add in lights and a sound effects that trigger whenever someone gets near the pumpkin. That's all well and good, but the real kicker here is ability to use custom sound effects. You could just use typical spooky sounds if you wanted, but it'd be a heck of a lot more fun to create some custom ones. Head over to Adafruit for the full guide to make it for yourself.
Halloween Pumpkin [Adafruit]