During the Flight 316 crash scene the plane makes noises like an empty barrel as if fuselage panels were banging against each other. Even in severe turbulence airplanes don't make such sounds. Usually it's just plastic panels squeaking and rattling.
At the start of the episode Jack wakes Kate up on the Island. Kate asks if they are back. When the scene is replayed later in the episode, when time catches up to the present time, Jack wakes Kate though she does not ask if they are back.
When on the plane sitting next to a nervous and excited Jack, Jack asks, "How can you read?" and Ben jokingly replies "My mother taught me." This obviously cannot be true as it is revealed his mother died after giving birth to him.
On the flight to Guam there is a lighted sign in the aircraft that says "No Smoking / Fasten Seat Belt / Use Seat Bottom Cushion for Flotation". Transoceanic flights are required to have life rafts and life jackets for every passenger. "Seat Botttom Cushion" equipped aircraft are restricted to overland flights and those that stay within just a few miles of the coastline.
The Aircraft they take to Guam is a Boeing 737, Distance to Guam is well over 6100 NM, almost more than twice the maximum range of this aircraft. Further, the cockpit scene shows 3 thrust levers, while the Boeing 737 only has 2 engines.
In the beginning of the episode, Jack dives from a very high height - maybe 50' or so - into the lagoon, then finds it to be shallow enough to stand up in. In reality, diving from that high a height into shallow water would likely result in a broken neck - the water would not be deep enough to cushion the impact.
During the flight back to the island, Jack is nervous and asks Ben "How can you read?" Ben calmly responds "My mother taught me." Ben's mother died during Ben's birth. This is not an error. Ben was merely being flippant with Jack.