This makes a great costume. Take a huge pumpkin and scrape out all the insides (make pies or soup with the insides). Cut a hole underneath the pumpkin that's big enough for your head to fit into it. Then carve out the face (make it really scary).
Wear a black cloak covering your whole body and slip the pumpkin over your head. Stand at the door and welcome your guests!
To make your pumpkin-head be seen even in the dark, coat it with a layer of glow-in-the-dark paint (glow-in-the-dark paint is usually transparent so the orange of the pumpkin will still be visible).
Thanks to Sundara for this great idea!