Regina's Engagement Ring

In The Stable Boy, Daniel proposes to Regina and places an engagement ring on her finger. At the end of the episode, Regina can be seen through her window in Storybrooke kissing the ring.

Later, in An Apple Red as Blood, Regina needs magic to make Jefferson's hat work. Seeing that the trinkets she's offered don't have enough magic, she takes out her engagement ring. Looking at it, she sees Daniel's face glowing inside the ring. She sacrifices the last bit of magic in the ring to retrieve the poisoned apple with the Sleeping Curse.

Trivia
Sacrificing the magic will leave a hole in the ring where Daniel's face once was - yet another reference to the hole that Regina's revenge will leave in her heart.