The couple lives in a sprawling $8 million home in a luxury subdivision with its own airstrip near this small town. Jett died at the family vacation home in Grand Bahama last week.
More than a dozen reporters and photographers gathered outside the Jumbolair Aviation Estates subdivision hours before the afternoon event.
A steady stream of catering trucks and florists entered the complex Thursday. A handful of locals also stopped by out of curiosity or carried bouquets of flowers and handed them to guards at the subdivision's main gate.
"I wanted to help John celebrate his son's life and not necessarily his death," said 52-year-old Sherie Maud of Ocala, who brought a dozen red roses.
A sign outside the Saddle Rock cafe in town, where Travolta often stops for a western omelet, read: "Condolences to John and Kelly."
The service for Jett was to adhere to the tenets of the actor's faith, Scientology, and celebrate the teen's life.
Tommy Davis, spokesman for the Church of Scientology International in Los Angeles, said Scientologist funerals or memorial services are more like a "celebration of their life, an acknowledgment of their life, and it's a way to wish them well in their future life.
Davis said Scientologists believe that a person is an immortal spiritual being, and one's spirit is reborn in another human body.
"The word reincarnation is a term often used loosely," Davis said. "We call it 'past lives' in the sense that one is living lifetime after lifetime."
It was unclear whether any celebrity friends were attending the service. Travolta, an avid pilot, bought the house because of the community airstrip and visitors can fly in and out without being seen by paparazzi, who have staked out the area for days.
The Travoltas have spoken publicly only once since their son died. "We are heartbroken that our time with him was so brief. We will cherish the time we had with him for the rest of our lives," Travolta and Preston said in a statement Sunday.
Jett Travolta had a history of seizures and was found unconscious Friday in a bathroom.
Doctors in the Bahamas performed an autopsy Monday but did not release results. A Bahamas undertaker said the teen's death certificate listed "seizure" as the cause of death. The body was cremated Monday and flown to the U.S. the same night.
Earlier Thursday, Travolta's friend and fellow Scientologist Tom Cruise told ABC's "The View that Jett's death was "horrific."
"John just adored him, both of his children," Cruise said haltingly. "... It's something that I don't have the words for."