A cross necklace search like a search for a crashed plane in desert simile
Oliver compares his search for Evie's lost cross in the forest next to the Old Bridge to searching for a crashed plane in a desert. He finds much significance in such a measly task. Evie lost her cross necklace while she was riding with Robert which makes the task that much more ridiculous and Oliver naive.
Sound of motor bike like sound of a rocket simile
While searching for Evie's cross necklace Oliver is surprised by the sound of a motor bike that sounded like a rocket interrupting his thoughts. Oliver and Evie are on the bike and Robert starts mockingly addressing Oliver.
Evie-the ripest apple on a tree metaphor
Evie is starting to pay attention to Oliver and he is feeling out of himself. It makes his ego stronger that he is getting the admiration of this girl that is known by everyone in the town. To his youthful and blind sexual drive she is the ripest apple on the tree and she is giving his attention to him.
Fly in a treacle simile
Imogen is Oliver's hopeless and one-sided love. In fact, Imogen is engaged and about to get married, a fact which brought immense misery and despair to Oliver. Now, that he finally has a type of a relationship with another girl he finds himself daydreaming about competing with Imogen and her fiancé. This makes him compare his situation to a fly in treacle.