Simile.
An example of a methaphor that the author uses in the book is "I'd die without Rowley". He's over exaggerating what he would do without his bestfriend. Who would actually die because their bestfriend is gone?
Metaphor.
An example of a simile that the author uses in this book is "Having a corn dog for breakfast is just like heaven". He compares the feeling of eating a corn dog to the feeling of being in heaven.