At dinner, when Elena mentions Bonnie is descended from a long line of witches, Stefan says that he knows there was "a history of Celtic Druids that migrated here (Mystic Falls)". In the books, Bonnie's magic powers come from her Druid family line. She's also fair and red-haired.
The first time the pupil change was used to show compulsion.
Bonnie is shown driving a silver Prius. But in episode 1 she is driving a blue Prius.
Stefans number on his football jersey is 17
This football themed episode is titled "Friday Night Bites" which is a nod to the movie and tv show "Friday Night Lights". Fun fact: Zach Roerig (Matt) played Cash Waller in the beloved tv show, thought in that, he was a rodeo cowboy and didn't actually play any football.