Eloise said they need to repeat their last flight which is why Jack needed to give John his shoes, along with Hurley taking a guitar just like Charlie, Sayid being handcuffed and seated next to a Marshall just like Kate, and Ben being late just like Hurley.
The reason Christian is wearing the white tennis shoes instead of normal dress shoes is explained in this episode.
While he is waiting to board the plane, Hurley can be seen reading the graphic novel "Y: The Last Man." Its author, Brian K. Vaughan, has been a co-producer on a large number of Lost episodes (although not this one).
WILHELM SCREAM: The scream can be heard as the flight attendant is being tossed against the cabin wall.
Jack is seated in row 8 on the plane, Kate and Hurley are in row 4. These numbers are both part of the Lost numbers sequence.