The Americanised (Americanized?) Halloween that we experience today actually originated in the Celtic fringes of Britain, and was adapted over the decades by Christian traditions, immigrants conventions and an insatiable desire for sweets.
The influx of Irish immigrants in the 1840s to North America could not find any turnips to carve, as was tradition, so they used the more readily available pumpkin into which they carved scary faces.
Nicholas Rogers, a historian at York University says that when people prayed for the dead at Hallow Mass, they dressed up. When praying for fertile marriages, the boy choristers in the churches dressed up as virgins. So there was a certain degree of cross dressing in the actual ceremony of All Hallows Eve