at around 40 mins) When Isaac is stealing the gift certificate from his deceased co-workers drawer, it can clearly be seen that it expires on 6/30/01, which gives another clue to the movie taking place years prior to its release date.
The restaurant that Sam works in is called Le Cafe Miro 81. This cafe was seen at the end of Final Destination (2000) in Paris. When looked at from this angle, MirO81, and flipped, it's another reference to "180" - a number referenced throughout the franchise.
A music video for the song "New Romance" by Miles Fisher starring the cast of Final Destination 5 was made to coincide with the release of the film, and can be found on YouTube. In true Final Destination fashion, the video has the cast meeting their ends in very grisly ways.
(at around 10 mins) The video that the office workers are watching on the bus is describing the corporate retreat company they will be working with. The company's name is "180 Corporate Consulting," another continuation of the number 180 in the series.
(at around 47 mins) At the spa, just before the needles are put on to Isaac, he jokes with the masseur saying, "All right, Let's do this! Two billion people cannot be wong" Apart from being a pun, it could also be a tribute to Final Destination's first part director, James Wong.
(at around 23 mins) At the memorial service, the second name on the plaque (also the second name read aloud) is Chris Boylan. This is a reference to Christine Boylan, wife of the film's writer, Eric Heisserer.
at around 1h 23 mins) Near the end of the movie when Sam looks at his plane ticket right before the crash the date is clearly displayed as May 13, 2000 Flight 180, 9:25 p.m. which proves the movie is a prequel to all the others.
Clues to the twist ending (linking to the first film) can be found by the request to turn off pagers at the beginning of the movie, the old-fashioned office phones, the clunky keyboard in doctor's office, the Liberty license plate (on the coroner's van) which was used in New York until 2001, and the song playing on the radio, "I Will Buy You A New Life" (Everclear, 1997).
Most of the death sequences are based on real-life incidents. The opening bridge collapse is inspired by the Tacoma Narrows Bridge. Additionally, someone has died from an acupuncture needle stabbing into their heart after falling off the table.
at around 44 mins) Before she leaves the office, Olivia knocks over a frame with a picture of her in it. The crack in the frame is centered on her right eye. This is a foreshadow of what happens on the eye surgeon's table.
In the Final Destination 5: Circle of Death (2011) special feature it is said that some of the actors from the first Final Destination (2000) were brought back to film the airplane scene but this is incorrect. Their footage was actually green screened into the film.
at around 25 mins) At the memorial when Isaac's name is announced and laughed at. What is said after is another hint alluding to it being a prequel. "I see dead people" is a famous quote from The Sixth Sense (1999) which in the time line would have just been released the year prior.