What is the proper way to sell things in a Yeshivah canteen on Shabbos?
The point of the canteen is to give access to kosher food to the students that need that availability. There is also a point or ticket system that they are rewarded with, that they can redeem in the canteen. They can get food with cash as well.
They can pick up items in the canteen and pay after Shabbos. They should not mention price or measurement.
The canteen should find a method of keeping a record through paperclips etc.
Using points is OK. But it is questionable whether one may use special Yeshiva dollars or vouchers. See here for more on that.
וראה שו״ע אדה״ז סי׳ שכג.