The Paperbag Princess by Robert N. Munsch
Elizabeth is a beautiful princess who lives in a castle and wears fancy clothes. She is about to marry Prince Ronald when a dragon smashes her castle, burns her clothes with his fiery breath, and takes off with Prince Ronald. Elizabeth only has a large paper bag to wear but sets off to find the dragon and reclaim her prince. She outsmarts the dragon and rescues Prince Ronald. But the spoiled prince says "Elizabeth, you smell like ashes, your hair is all tangled and you are wearing a dirty old paper bag. Come back and rescue me when you look like a real princess." Elizabeth immediately realizes that her ending will be much happier if she does not marry such a brat.
I have long felt that this, his first book ever, was Robert Munsch's strongest story. While I like some others, this one has the components of a strong plot, a great character and a fun, twisted ending. Hurray for Elizabeth. A great read aloud!