Brenda is a vegetarian. Bill has an uncle in Maine who owns a cabin. Marcie has a recurring nightmare about rain. Steve has been working on Camp Crystal Lake for over a year. Alice is an artist.
Bill plays guitar.
The most revealing scene in the film comes when Ned watches Jack and Marcie frolic in the distance. Ned's loneliness does absolutely nothing to advance the plot, but is a very nice touch of characterization - screaming aside, most slasher movie directors don't go out of their way to show emotion, especially subtle emotions like depression or loneliness. Granted, it's not much, and if you leave the room to get popcorn for five seconds you might miss it, but Ned's loneliness is a nice bit of characterization, a small gem of personality in what could otherwise be a pointless blood-fest. As a mystery, Friday fails miserably. It's goofy, but, somehow, it works.