Life is a box of chocolates.
This is a metaphor as it means much more than just a saying of what the phrase is. Elton John is comparing life to a box of chocolates to say that life is full of surprises and unexpected events.
Simile:
She was a girl like a cat in the rain.
This is a simile as it compares a girl with a cat. The simile is used to show that the girl is independent and doesn't need anyone else to take care of her.