Rejoinders are short "memorized expressions" that let a listener show their emotion to what they're hearing. Why just answer with "oui" or "non" when you can say "Quelle surprise!" or "Non, c'est pas vrai!".
Here's a PDF of 100 French rejoinders and text-speak abbreviations. Each slide has 2 half-sheet posters with French expression and the English translation. They are created on colorful backgrounds, and are color-coded to the category of rejoinder (agreement, doubt, praise...) I am including the PowerPoint version too, so you can edit if you wish.
Just print, cut, laminate, and get your students using French from day 1