On the topic of francophone traditions and festivals, I was lucky to witness the terminale (year 13) students in Nancy celebrating 'percent' (or 'Père Cent'). This tradition marks the start of the 100 day countdown to the bac exams (the French baccalauréat is the equivalent of A levels in the UK). I was told that this festival is particular to the Lorraine region/North East France, but I think that certain other regions celebrate it too (e.g. Bordeaux).
Although Père Cent is nowadays a student tradition, it has its origins in the French military. France used to have a conscription system (compulsory enlistment in the armed forces) and the soldiders would celebrate the 100th day before they were released from their obligatory military service.
The passage below is taken from a Wikipedia entry explaning the etymology (origin and meaning) of the phrase 'Père Cent':
(Militaire) (France) Fête de tradition qui se déroule cent jours avant la libération du contingent.
Cent jours avant la libération, les appelés enterrent le Père Cent. (...) Le Père Cent est joué par un soldat ou représenté par un mannequin. (...) À la fin du défilé, le Père Cent est pendu, puis brûlé. — (Béatrice de Villaines,Hugues de Champs, Les saisons de la vie, 2002)
(Par suite) Fête de tradition lycéenne française qui se déroule cent jours avant le baccalauréat.
Il s'agit d'un phénomène collectif local appelé communément le "Père Cent" ou "les cent jours du Bac". — (Michèle Cros, Daniel Dory, Sylvie Besse, Terrains de passage: rites de jeunesse dans une province Française, 1996)
The celebrations involve dressing up in costumes, skipping class and going around town in big groups, throwing eggs and flour in the streets. Obviously, this can lead to trouble and the local authorities in Nancy have tried (unsuccessfully) to stop the festival taking place. One of the teachers in my school told me that the Mairie de Nancy had spent around 10.000€ last year cleaning up the mess left by the students.
In spite of this, it does look like a lot of fun and is considered a right of passage for students - kind of like an unofficial marker of their transition into adulthood. I've included some useful articles which explain the tradition in more detail, as well as a video of a parade of students outside my lycée.