As a Foreshadowing page, all spoilers are unmarked as per wiki policy. You Have Been Warned!

Deaths

Alex Browning

A very subtle example is that when Terry dies, her blood sprays onto Alex's face with the blood stain on his right cheek in the shape of a "7". This later becomes a plot point where Alex thought he was the sixth to die but since he never moved from his plane seat like in the premonition, he's actually the seventh and final person on Death's list which means Clear is next and Alex has to rescue her.

Tod Waggner

Tod's name is German for "Death", a foretelling sign that he doesn't last long in the movie.
A skeleton figurine hanging in a noose is among the toys scattered around Alex's room. Tod accidentally gets strangled to death due to a bathroom slip-up.
On the plane, Tod performs a hanging gesture to warn Alex not to changed seats with Blake and Christa.
In the opening disaster, Tod is killed first when a stereo whacks him on the head. This foreshadows how he'll be the first to die after the accident with Tod even using a radio similar to the one in Alex's vision.
Tod used the toilet before the plane explosion and dies post-premonition in his bathroom.
While Tod's death was in motion, an owl lands on a tree branch outside the window of Alex's bedroom. In many cultures, owls are viewed as omens of death.

Terry Chaney

One of the books on Alex's bookshelf was Death of a Salesman in which the titular character died in an automobile accident. No guesses as to what happened with Terry.
After the plane exploded and the scene cuts to the individual reactions of the survivors, Terry's scene has a picture of a bus behind her in the background.
The colored line scheme of the plane's fuselage was similar to the one on the side of the bus that killed Terry.
Alex spots the reflection of a bus on the coffee shop's window yet sees nothing when looking in the street, reflecting how the bus that hit Terry came right out of nowhere.
Alex asks Clear, "How do we know that by sipping this coffee, or breathing the air, or even crossing the intersection... we haven't started in motion the events that will someday lead to our deaths." Fittingly, Terry's death happens as soon as she steps out onto the intersection.
The song "Into the Void" playing on Carter's car radio contains the lyrics "final destination" right before her death.
Terry's last words were "You can just drop fucking dead" which she ironically did precisely that not a second later.

Valerie Lewton

In the opening sequence, there's a picture of someone getting struck with a knife in their chest, foreshadowing Ms. Lewton's fate.
Ms. Lewton's front door has stained glass that's prominently colored red and orange with a dagger design, echoing the house fire and the kitchen knife that ended her life.
Freaking out over the school logo on, she told herself "Soon you'll be gone, you'll be gone." Little does she know that she won't be departing to a new school but the afterlife.
The woman on Alex's TV before he went to Ms. Lewton's house said the line "That's a huge knife set." When an injured Ms. Lewton went to reach for the towel resting on her knife rack, it tipped over and a large knife gets lodged in her chest.
After pouring herself a drink, her mug cracks and starts dripping liquid on the floor. This is similar to what happened to her when her computer exploded, sending a shrapnel that cut her throat and spilled her blood across the floor.
Ms. Lewton's rather rude response to the man who hands Alex a pamphlet at the airport by mouthing "fuck you" after she's told him off. This would indicate her sudden shift to an antagonistic attitude towards Alex when she blamed him for her husband's death even though he saved her.

Carter Horton

After Terry's death where her blood sprayed everywhere, the bloodstain on Carter's jaw looks like the number "4" upon closeup. He was originally the fourth survivor to die, but Alex saved him at the last second.
Carter almost died when a train ran his car over but Alex saved him at the last second by tackling him to the ground. In the end, Carter returns the favor for Alex and performs the exact move from a falling sign in Paris.

Billy Hitchcock

During the opening credits in Alex's room, the camera lingers on a French history book turned to a page with an image of a guillotine. This is an allusion to Billy dying via head decapitation.
After barely passing his driver's test, his instructor told him, "Young man, you're gonna die a very young age." Although he was not the one driving, Billy's eventual death involved a car.
While he is looking through the terminal window when the flight takes off, the plane's reflection is shown flying across his face. Flying in a line marking the exact spot where the piece of the car shrapnel slices and decapitates him later on.
Carter punches Billy's mouth and leaves a sore on his lower lip which looks like blood dripping down his chin. This is what happens when Billy loses the top half of his head.
While Billy, Carter and Clear are driving to Alex's home, Carter sarcastically threatens to "kill Billy" when he constantly expresses fear of his imminent death. Carter's subsequent actions would then indirectly cause Billy's death.
Billy's hat falls off his head during Carter's attempt trying to "take control", mirroring the top half of Billy's head falling off the bottom half.

Clear Rivers

When Alex is using a cigarette lighter, there's a spark that looks like lightning which later alludes to the live wire and lightning storm that tried to kill Clear.
After the Flight 180 catastrophe, behind Clear is an orange and red picture that echoes both the plane explosion and the car she almost got blown up in.
Clear was originally supposed to die from an explosion while on board Flight 180 if it weren't for the intervention of Alex. He would later intervene again from an explosion in her car.