Samhain has it's origins in the British Isles, while more modern traditions like trick-or-treating developed in the United States. Most are based on folk customs brought to North America with the Irish immigrants sometime after the year 1840. The holiday most today celebrate as Halloween actually has a very long history, one which stretches back to a time of the ancient Celtic religions. For them the evening of October thirty-first and the morning after a Sabbat they called Samhain marked the beginning of their New Year. Primarily it was celebrated as the "Feast of the Dead". Since the New Year began in winter a season known for death, it's really only natural that the Celts would have honoured ( and ward off) those who had passed on, they also celebrated in ways of divination, through rituals, and spells. The Celts also took some time for their earthly needs such as; hiring servants and slaughtering their live stock to make food for the winter.
For early Europeans it was celebrated in many of the same ways. Making the beginning of winter, the cold and the lean months ahead. Their flocks were brought in from the fields to live in the sheds until Spring. The third and final harvest also took place at this time and was incorporated into their celebrations. Many Pagans did and still do decorate their altars with symbols of the season such as but not limited to; wheat and various fruits and vegetables. To some the harvest is interpreted more abstractly, symbolizing your gains and achievements over the past year.
In the second half of the nine-tenth century, America was flooded with immigrants. Most of which were Irish settlers, fleeing the potato famine of 1846, these people help popularize "Halloween" as we know it today on a national level. Borrowing from the Irish and English traditions, Americans began to dress up in costumes, going door-to-door asking for food, and sometimes money, a practice which became what we now call trick-or-treating. In the late eight-teen hundreds, there was a move in America to mold Samhain into a holiday more about community and neighbourly get together's, rather then about our ancestors, or witchcraft and pranks. By the turn of the century, Halloween parties for both children and adults had become the most popular way to celebrate. Parents were encouraged by newspapers and community leaders to take anything magickal or frightening out of Halloween and instead focus on parties, with food and costumes. Because of these relentless efforts Halloween lost most of it's superstitions and religious overtones by the late twentieth century. In 1921, Anoka, Minnesota celebrated the first official city wide observation of this holiday. There celebrations included a pumpkin bowl, a costumed square dance and two parades. After this happened it didn't take long for this holiday to catch on nationwide. New York joined in on the festivities in 1923, soon after was LA, in the year 1925. By then most of what Pagans consider important at this time had vanished, left only in some jaded traditions, changed by those who feared anything different or magickal. However for those who did practice the older religions, they kept their traditions alive through family and friends, rituals were still held and divination was still as popular as ever.
Since we are not from ancient Celtic times, it should be obvious that we wouldn't celebrate exactly as they did. Much of "neo-paganism" is a reconstruction of what is believed the pre-Christian religions were like, based partly on anthropological and historical research, and partly adapting the old religions ideas, but mixed with our modern culture.
Today Samhain is still one of the most important Sabbats, for most Pagan religions. Pagans participate in modern Halloween festivities along with rest of North America. The difference is those who follow the Pagan life also incorporate their own spiritual traditions. For them Samhain marks the most magickal night on the wheel of the year. It is the dark twin of Beltane, for most it is known as Halloween a night of trick-or-treating, dressing in costumes and telling creepy stories. Although many Pagans celebrate in the same way, they add things like seances, tarot reading and scrying to their parties. Most will perform rituals with their coven or alone, they will also do spell work. For Pagans today Samhain is a time to confront their personal and cultural attitudes toward death and those who have already passed on. It is a time to deepen our connection to the cycles of the seasons, to the generations that came before us and those still to follow, also to the Gods and Goddesses we worship. It is also a time to let our inner children play to pass on our childhood traditions to our young ones and to share the fun with our friends and neighbours of all faiths.