Henry reaches level 23 while playing a video game. He also mentions reaching level 16. 16 and 23 are the fourth and fifth of the Lostnumbers. (Level twenty-three is also a nod to the official Disney fan club D23.)
In the first scene at the sheriff's station, the clock shows 8:15, a reference to the flight number from Lost.
Ingrid says to the foster children that light will be off in fifteen minutes, a reference to the third Lost number.
Ingrid tells young Emma that there are fifteen subconscious signs or tells that a new foster child displays when they're going to run away on their first night in a new home; a reference to Lost number 15.
Henry mentions that Regina uses his birthday for her passwords, including the one for the ward, and, since Regina enters '815' to get into the ward in A Tale of Two Sisters, his birthday is confirmed to be August 15, or 8/15, which is a reference to the first two Lostnumbers.
When Ivy enters the pub, Roni is pouring four shots of MacCutcheon Scotch Whisky, a fictional brand on Lost. However, when she sees Ivy, Roni removes the bottle and snidely remarks that they have a strict "no whisky for witches" policy.
↑ 1.01.11.21.3Keily, Karl (October 15, 2011). NYCC | Once Upon a Time Pilot Screening and Panel. Comic Book Resources. “After the screening Kitsis and Horowitz briefly discussed the show with the audience, revealing Once Upon a Time will include many Easter eggs from Lost. They specifically cited Emma Swan as being named after the island's Swan Station, the town clock being stuck at 8:15 (an allusion to Flight 815), and a character's house number being 108 (the sum of the six recurring numbers from Lost).”
↑Loggins, Emma (September 5, 2012). Jennifer Morrison On Being The Skeptic In ‘Once Upon A Time’. Fanbolt. “Jennifer Morrison: I think [show creators] Edward Kitsis and Adam Horowitz knew what they were doing when they named her Emma Swan. They told me they thought it was a cool name and they were moved by the idea of The Ugly Duckling story, so it appeared to fit.”
↑ 4.04.14.24.34.4Abrams, Natalie (March 1, 2018). Once Upon a Time bosses drop major detail about series finale. Entertainment Weekly. “Speaking of Lost, the OUAT bosses reminisced over a number of references they've slid into the show over the years. There have been Apollo bars, of course, but Once also included Mr. Clucks this season — and had Daniel Dae Kim voice the drive-thru guy. Emma's VW Bug is a reference to Hurley's van, and even their former Lost bosses Damon Lindelof and Carlton Cuse have done voiceovers as a weatherman and a DJ.”