As the title says, I want to know what and where happens on class reunions, cause I'm still in high school and if I would be doing something there it would be going home. Put simply, I need ideas less generic than what many jp novels and manga show (like, chatting idly, cause not much else seems to be happening most of the time).
For further context, the mc is a not very sociable girl (though she is not a shut-in, just doesn't like talking with people pointlessly) who is going to a class reunion party alongside her friend, who is more on the extrovert side. She's nineteen, so past the legal drinking age, and she lacks a forearm. Setting is similar enough to modern world that it doesn't change anything.
Ai-chan's first class reunion was held when Ai-chan was 25. That's 8 years since Ai-chan graduated high school. While you can make class reunion happen after graduation, since there is no set rule on when class reunion should be held, it normally wouldn't be held that early. You'd have your classmates busy with college, working part time jobs and maybe trying to find out what they want to do with their lives.
In general, they'd be either far too busy or far too reluctant to join said reunion. For those busy with college, they'd be far too broke to travel back to their hometown just to meet their 'friends' who they'd rather not meet again, at least not so soon. For those working part time jobs, they wouldn't be able to get a day off just for a reunion, and they'd also be reluctant to meet people they'd just met a year earlier instead of, you know, making ends meet. As for those who are still trying to find out what they want to do, they'd also be reluctant to go to such reunions, as they have nothing to brag about.
Class reunions are held usually around 5-15 years afterwards. Ai-chan's mom had her class reunion 60 years later, some of the classmates are already buried and rested in peace. What people do there? Reminisce old memories, there's fun in recalling fond memories that you reconstruct years later with your friends help. You also tell people what's been going on with your lives, such as getting a job, getting married, having children. Or you flex on your superior prowess such as getting a new house, getting a sports car, buying a yatch, having a Forbes 500 company or in Ai-chan's case, brag about legally having a lesbian wife to Ai-chan's all-girls school classmates.