Halloween is not a Jewish holiday. You should go to work as usual. And don't fast.
However, I have just thoroughly researched both the Jerusalem and Babylonian Talmud and I can't find a single prohibition about Jews engaging in trick-or-treat activities. So, halachically, sure it's OK, as long as your neighbors don't distribute pork chops or bowls of young stewed goat in mother's milk sauce. If they do, cite Exodus 23:19 and ask if you could have a Hershey bar with nuts instead.
Doctrinally, Halloween games are OK, but philosophically, it's a very non-Jewish holiday because the air is full of witches, spooks and spirits. And they're not singing "Adon Olam," either. Witches, in our Bible, don't get very good press because, basically, it was a heathen occupation. It still is. You never hear a Jewish mother say, "Well, your daughter may be the best pediatrician in town, but my daughter's a very successful witch." And in the Chumash (the five books of the Torah), statements about these evil creatures are usually linked with stones, as in, "she shall be stoned to death."
But if you do let your kids loose on Halloween, I'd suggest that when they come home with bulging pillowcases, you balance the evening with a reading from Samuel. It's a spooky story and if you read it well and let them nibble on the loot as you read, you can capture their childish attention.
It's a darkly dramatic tale of Saul and his troubles. Poor Saul, the first king of Israel. Whatta job. Long hours, horrible longevity, no pension benefits. But plenty of nachas for his mama. "Oh your son's a doctor, how nice. My boy, Saul, is the first; the one and only King of Israel."
But Saul is a tragic figure. Modern biblical scholars tell us he suffered from epilepsy. How'd you like to tell the Philistine ambassador, "No you can't see the king today. He's having a fit."
Even worse, Saul's gotta worry about young David as a rival. Furthermore, his own son, Jonathan, seems to have a passionate attachment to his competitor. These are personal problems. But politically, he's in deep chullen, as they say in the Negev.
There's this war with the Philistines. And the Philistines are an advanced society, at least technically, because they know how to work iron. Their swords and shields and daggers are sharp and hard, unlike the bronze banana weapons of the Israelites. They've got an edge — so to speak. Maybe the Israelites are better, at say, grape and olive culture, but wine and wheat cakes in olive oil make you logy and fat. Not great characteristics for soldiers who have to tramp up and down the hills of Judea.
Anyhow, the king is preparing to meet the Philistines at Gilboa and "his heart trembled greatly." He needs all the help he can get; from a roadside fortune teller, a shrink, or even the sorceress who lives in the village of Endor. He decides on the latter.
But Saul being Saul, nothing is simple. In line with the instructions of He who made serpents, shrinks and sorceresses, Saul has banned the profession of witchery, the only profession open to women except for that other one. It's as illegal as roast pork on the Friday night oneg table. So when Saul shows up at the witch's house and asks her to bubble her cauldron and read the future, she says, "No way baby — that stuff is against King Saul's law. You're just trying to get me in trouble."
"But I am Saul, the first and only king of the Israelites and I say it's OK. Divine unto me," says Saul.
The sorceress, who finally notices that her customer has on a golden crown and royal robes, yields. At Saul's request, she conjures up Samuel from his eternal sleep, which is not a bad trick from a small-town witch who hasn't had much time to prepare her props.
Saul kneels, puts his face into the dirt, and tells Samuel that the Lord has forsaken him.
And Samuel knows why: Because when Saul was told to utterly destroy the Amalakites and their possessions, he held back some sheep and oxen for sacrifice to the Lord. It is not clear why this is such a heinous crime. (Go read Samuel I, Chapter 15, and see what you think.) But that's a violation, says the resuscitated prophet.
Then he proceeds to tell Saul that tomorrow — the day of battle — will be disastrous. And so it is. Saul is killed.
We hear no more of the witch of Endor and her illegal profession. Most biblical scholars, both religious and secular, find it interesting that, though our book condemns the art of witchcraft, it tells this tale of supernatural power.
The bible, as usual, tells it like it is.