Late lunch/light dinner
One of the most pleasant things of the examination is late lunch or early dinner with the examiners and the custos. The student has to organize it at his or her own expense.
The logic is: these people have been using a whole day for the examination, i.e. given their time and expertise to the student. This is how the student gives a personal tribute to the examiner(s) and the custos.
Often, students take their immediate family with them. Sometimes, they also invite their best colleagues. But, this is up to the student.
This is time for going through the examination, your study, U.S. elections, whatever. It is time for relaxation and letting off steam and for creating a personal tie with the examiners.
Also, doing this before the evening party may save money: if you pay this, you do not have to pay in the evening. But, I am not sure whether this theory works.