Uh, isn't Halloween one of those pagan holidays that got "taken over" like Christmas and Easter?
That's how the story goes, pretty much.
Samhain, as a harvest festival, was also considered the time when the veil between worlds was thin. So people would wear masks (I forget why at the moment and I can't be arsed to look it up) and leave gifts of food for the mischievous spirits and such. Or, in essence, treats were given to prevent tricks.
Then it became Hallowed Eve due to Christian influence and somehow information got put into a blender and mixed up, and commercialism kicked in. And now it's Halloween.
The Samhain that pagans practice is different from the Samhain that was practiced in the past, because it takes an entire town to practice the old Samhain.
Christmas is an amalgamation of several holy days, though. One of them being Saturnalia (which is... Roman I think?), and another being Yule.
Still, even commercialized holidays can be celebrated without the commercialism. Sometimes the best Christmas is the Christmas where the presents were opened on Christmas Eve and you get to spend the day as a family, eating warm good food.