I often hear that my acquaintances pick up the bill for their underclassmans in their drinking session.
In this country, it is the convention that senior students treat junior students to drinking sessions.
I think the meaning of the convention must be to maintain the dignity of senior students by showing their financial power.
So, if one has something to do with underclassmans, he/she will meet the chance to treat them.
In club activities, it is inevitable to keep in good terms with junior students. It leads club members to spend a lot of money in the drinking session.
If you want to save money, it is not a good idea to join club activities.