Episode 1x03 -- "Friday  Night Bites"

"It's something that I've had forever and I never wanted to give it to anyone until now. I'd very much like it if you'd wear it for me...for good luck." ~ Stefan

Elena and Stefan hadn't been a couple for very long, but to protect Elena from his brother, Damon, the younger Salvatore gave her the necklace filled with vervain. As long as she wore the necklace, she couldn't be compelled. This necklace has been an important piece throughout the first three seasons of the show.