Festin literally translates to "feast". It's a beautiful word that evokes a sense of grandeur and celebration, much more than a simple repas (meal).
In this song from the movie Ratatouille, the word represents the ultimate dream of the main character. After a life of hunger and struggle ("affaibli par la faim" / weakened by hunger), the promise of a festin symbolizes hope, success, and the joyful beginning of a new life.
This song starts with a pretty bleak outlook! The singer, Camille, compares dreams to wine: "Ils donnent de la joie ou bien du chagrin" (They bring joy or sorrow). She then describes a life of hunger and desperation, having to steal just to get by because, as she says, "rien n'est gratuit dans la vie" (nothing in life is free). She's used to skipping meals and feels like she's losing at a bitter game. It's a tough beginning, painting a picture of someone who is lonely and struggling to survive.
But then, the whole mood flips! Suddenly, she's defiant, declaring that no one can tell her "Que la course aux étoiles, ça n'est pas pour moi" (That the race to the stars is not for me). This is a song about someone who refuses to give up, no matter how hard things get. She's ready to take flight and finally have her feast. The song ends with this amazing feeling of hope and celebration for a new life where she's finally free. The party is about to start, and "Le festin est sur mon chemin" (The feast is on my way).