Some will tell you that Halloween is the Catholic replacement for Druidic Samhain, a Celtic harvest festival. Not true. First, Samhain ceased when St. Patrick converted the Irish in the fifth century. Second, there was no Catholic holiday that replaced it. Third, All Saints was not established until the ninth century.
Rather, Halloween is the first day of Allhallowtide: All Hallows Eve (10/31), All Hallows (11/1), and All Souls (11/2). It was customary in historic Catholic Europe to have evening vigils with pious celebrations on the day before a major solemnities which is why Halloween exists at all. Immigrants celebrated and brought to the U.S. their vigil customs: Dressing up from the French; Jack-o-Lanterns come from the Irish, and from the English, begging door to door for "Soul Cakes," and promising to pray for the departed loved ones of those who gave treats.
Instead of allowing All Hallows Eve to glorify the violence, horror, and sensuality Catholics use this vigil as a time of fun and merriment, an occasion to make light of fears since Christ has conquered death, sin, and the devil. All Hallows Eve is a joyous time to prepare for All Hallows, to remember the calling to be saints and an opportunity for Evangelization by sharing about the true origins of Halloween.