Maybe as "Halloween," has origins in the Catholic faith. Hallows Eve on November 1 also known as "All Hollows Day" (or "All Saints Day"), is for the honor of saints. In 5BC Ireland, summer officially ended on October 31st. The holiday was called Samhain (pronounced sow-in), meaning "end of summer" - the Celtic New year.
During Samhain, Druids (being druids) believed that the dead would play tricks on mankind and cause destruction and bedlam. Folk would give the Druids food as they visited their homes to appease the dead- Hence how the trick or treat thing started...
The Bobbing for Apples thing happened when Roman Empire took control of the Celts - The Romans were worshiping Pomona, the goddess of the harvest. Apples were the sacred fruit of the goddess, and many games involving them entered the Samhain customs.
Now why so many Jack-O-Lanterns - Irish children used to carve out them out so to light them for Halloween. They commemorated Jack, an Irish villain so wicked that neither God nor the Devil wanted him (apparently there is a waiting list for both). As he was rejected by both, he wandered the world endlessly looking for a place to rest, his only warmth a glittering candle in rotten veg.Anyhoo I'm buying a large pack of lollies (candy) for any spook who may knock on our door for visit on Hallow's Eve...but I suspect it will only be a few drunks from the Riversdale pub or the crazy cat lady complaining my cat doesn't like to be petted. And he doesn't.