It's celebrated in a variety of ways and activities including trick-or-treating, ghost tours, bonfires, costume parties, "haunted house" tours, carving pumpkins (Jack-o'-lanterns), reading or telling scary stories, watching scary movies and so on.
There are several traditional games associated with Halloween. One common game is dunking or apple bobbing, in which apples float in a tub or a large barrel of water and the participants must use their teeth to remove an apple from the basin. A variant of dunking involves kneeling on a chair, holding a fork between the teeth and trying to drop the fork into an apple. Another common game involves hanging up treacle or syrup-coated scones by strings; these must be eaten without using hands while they remain attached to the string, an activity that inevitably leads to a very sticky face.