Not sure if it counts as a tradition, but my "StrangerVille Elite" club, consisting of sims who have solved the mystery or helped someone else do so, meets every Thursday evening at the Old Penelope bar for a fun night out. That is, when I actually think of it. Since there is no option to set club meetings on a specific day at a specific time (or at least not that I know of), I sometimes forget.
As for individual families, my very first TS4 household, consisting of five sisters / cousins, used to live together in a house and call themselves the witches of Willow Creek until they all got married and/or moved out to start their own lives. However, to show that they're still one big family, the handywoman among them carved and preserved Halloween pumpkins for everyone, with different colours and motifs depending on their personalities, and now every sister has her respecitve pumpkin sitting on the chimney of her living room in her home. I'm thinking about adding more family items of this kind, since every sister has a different talent, so I could have the artist paint individual paintings for every household next, for example.
