L'expression du samedi!
À la bonne franquette is an expression used in relation to an invitation to lunch or dinner. The host wants to let his guests know that the dinner will be informal and that guests are even welcomed to bring a dish if they want to. An English word that expresses this meaning is potluck.
A woman invites a friend and her husband over for dinner tonight:
"Vous venez dîner ce soir?" (Are you coming for dinner tonight?)
"Oui, avec plaisir! Mais on fait simple, d'accord?" (We'd love to! But let's keep it simple, okay?)
"Oui, oui. À la bonne franquette!" (Yes. Let's have a potluck)