Originating in the Celtic festival of Samain, Halloween was once a celebration of the end of the harvest. The Gaels believed that on October 31st, the boundary between the living and the dead opened, and the dead were able to walk the earth, causing sickness and crop damage. Gaels would light bonfires made of the bones of slaughtered livestock and people would wear costumes and masks to placate the spirits of the dead and sometimes to walk among them.
Pumpkin carving dates back to an Irish legend of 'Stingy Jack', farmer who tricked the devil to climb a tree, and then trapped him in the tree by carving a cross on the tree. According to legend, the devil cursed 'Stingy Jack' to walk the earth carrying a lantern carved out of a hollowed out turnip. Jack-O-Lanterns have since been carved from rutabagas and pumpkins as well. Ancient Celts used the "head" of the vegetable to make lanterns to frighten off evil spirits, and when people came to America, they discovered that pumpkins were easier to carve, made better lanterns, and probably looked scarier when used as a flaming head for Ichabod Crane's horseman.
So what does this have to do with our own tradition of buying the best candy to give to little children who are dressed as Power Rangers and Thomas the Train? No clue. I would like to see more turnip carving. Pumpkins should be saved for the raccoons. They have traveled a long way.
