If you liked "Jaws" T-shirts and "Star Wars" dolls, you're apt to love the new film by Wes Craven, the low-budget horror film director whose last outings were "The Hills Have Eyes" and last year's "Deadly Blessing," an unnerving little film that picked up lots of unexpected praise. Craven's next release is "Swamp Thing," a horror movie based on old comic strips. The film has yet to open nationwide, but it's currently showing in more than 200 theaters across the southeast. And shortly after a few special New York screenings two weeks ago, the filmmakers announced a $5-million string of commercial tie-ins that might make George Lucas envious. Of course, we'll soon be seeing "Swamp Thing" T-shirts, novelizations, reissued comic books, souvenir programs, poster magazines, soundtrack albums and books on the making of the film. But that's just the more mundane tip of Craven's iceberg. The merchandising tie-ins will also include a Saturday morning cartoon show based on the film, an art portfolio book, a children's how-to book called "Makeup Magic From Swamp Thing," bubble gum cards, Halloween costumes, pajamas, underwear, drinking cups to be distributed by 1,500 convenience stores, and green "Swamp Thing" T-shirts that change color as body temperature changes. If all this goes along with the latest from a low-budget horror movie director, what's going to happen when the next "Star Wars" installment comes out?