As you may or may not already know, Princeton has a bit of a different system for dining once you become an upperclassman. The one that probably draws the most intrigue from prospective students is what is known as an "eating club." There are 11 of these clubs, and each one serves as a form of social and dining scenes for upperclassmen, should they choose to be in one. Certain clubs are "sign-in," where one simply has to write their name down in order to join. Others require students to go through a process called "bicker," where students are chosen by current club members to be a part of a club.
Sophomores go through the bicker and sign-in process for the various clubs in the spring semester. The bicker process usually involves playing games and doing mini interviews with various members of the club for a few hours in the evening. This allows you to get a feel for if the club is right for you and provides an opportunity to learn more about the club as a whole. It lasts two days and on "pickup day," students who bickered are notified of their status in the club; if accepted, they proceed to their new club and are warmly welcomed by other club members. Because sophomores aren't upperclassmen, they are allowed to have a couple of meals at the club per week and will then have full member privileges once their junior year starts.
Eating clubs are a great way not only to eat and socialize with your current friends but also provide a great opportunity to meet new people and make new friends. It's just one of the upperclassmen dining plan options, but worth giving it a shot if you're even the slightest bit curious.