When Cristina finally comes out of her catatonia, she tells Owen they ran out of water. Yet in the season 8 finale, when the crash survivors are in the woods, you can see a stream nearby in several shots. Not only would it have provided water, it probably would have yielded fish too. And they had a fisherman with them.
When Derek is viewing the wreckage of the plane, he has flashbacks to events he didn't witness, such as Lexie's death.