As Leo and Stargirl begin spending more and more time together in chapter 17, he begins to understand that her actions seem genuinely motivated by a desire to make others happy.  On a walk in chapter 20, Leo is finally starting to notice things the way Stargirl seems to notice them.  It is during this walk (in chapter 20) that Leo tells Stargirl he wants to be a TV director when he grows up, and she tells him she wants to be a "silver lunch truck driver."

Out of a genuine appreciation for others and desire to make them happy, Stargirl dreams of owning an entire fleet of silver lunch trucks, which she will use to bring lunch to hardworking people everywhere.  They, in turn, will be astonished by the variety and quality of meals she provides.  Part of this dream comes from Stargirl's large imagination and ability to think outside the box.  Admittedly, this is a strange aspiration, for anyone, in answer to the question of life and/or career goals.  But as it reflects her creativity and quirky personality, it also shows her heart and ability to think of unusual ways to bring people joy.