Go to Theatre Three. It's a very old, small threatre that's been restored. They host both children's and adults plays. Their annual randition of "A Christmas Carol" is a must see. The theatre is beautiful, and there are few originals on Long Island like it. The actors are very skilled, and you will see a lot of the same actors in different plays. The theatre has a very 1930s feel to it, its marvelous. They also offer acting lessons, and you can hold events at the theatre. I had a birthday there when i was little, and at the end the actors took me on stage and sung happy birthday to me :)
The Dicken's Festival happens the first weekend of December each year and the entire town is given over to the celebration of history and culture. People dressed like Dicken's characters from his books wander the streets, restaurants and shops and talk to visitors, patrons and diners.
The three things I like best about the festival are:
Harbor Ballet Theatre's "The Nutcracker" which is staged at the Port Jefferson High School auditorium with performances on Friday evening, Saturday afternoon and evening, and Sunday afternoon. The company has local students from various dance schools participating and the leads, Cavalier and Sugar Plum Fairy, have often been dancers from the New York City Ballet.
Theatre Three's "Christmas Carol" which has performances throughout December.
The Port Jefferson Historical Society's Candlelight House Tour which features different homes each year.
These are all not-for-profit groups that deserve your support.
Theatre Three in Port Jefferson, in an historic cinema building, provides a delightful evening of theatre or a late evening in the second stage Griswold's cabaret/bistro (beer and wine is now available as well as coffee, soft drinks and snacks) where intimate performances of music, song and cabaret entertainment are outstanding.
Everyone in cast, crew and patrons know each other and make strangers feel welcome the first time they come to the main theatre or the second stage.
There is a children's theatre that runs delightful productions for young children as well, and there are also occassional art cinema movies shown.