Schools - host costume parades on Halloween day, especially if you can arrange to tour through one of the decorated home sites for that year. Or, host an in-school costume contest with the entry fee of a non-perishable food item.
Fire Departments - Host trick-or-treaters with a haunted firehouse or help keep trick-or-treaters safe from traffic hazards throughout your town.
Church Groups - distribute cider and doughnut holes or other snacks to hungry trick-or-treaters or collect food for delivery to the food pantry at the end of the evening.
These are generic suggestions. A school can hand out cider or a fire department can host a costume parade. Your participation is limited only by your imagination.