The informal economy is economic activity that is not taxed or monitored by the government. Students in a university or college setting often establish networks related to the informal economy with other students or sometimes with faculty and staff at the college. They don't often extend this network beyond the confines of the university.
Students are often expected to contribute to the shared costs of something, such as a ride. For example, Boston University's RideShare program (see the link below) is an electronic database that connects people who are going to the same place. They can share the cost of gas and tolls (and, if traveling in a rented car, the cost of the rental). This database is only open to people in the Boston University community--not to people beyond the community. Boston University students can also use the website called ULoop (see the link below) to find used furniture or other items such as equipment and clothes, and they can also find notices posted in their dorms or other public places advertising low-cost or free clothes or other items. Some of these items might be exchanged or given away, and others cost money (but they are not generally taxed). Boston University's Facilities Management office (see the link below) also provides surplus furniture for free, and there is also reduced-cost recycled furniture sold on the campus. These items are designed to reduce students' carbon footprint.
These programs are just examples of the informal economy at one university. At other colleges, students may exchange labor, such as fixing a computer, in exchange for goods or for food and drink. Food, drink, and labor are often exchanged for free among people who are already friends or know each other well. Some students will simply give the clothes, books, or furniture they don't need to other students. This is particularly true of graduating seniors who give these items to younger students who are not yet graduating.
These exchanges show that most college students are concentrated on acquiring items related to their studies and living expenses, such as furniture, clothes and books, and related to entertainment, such as food and drink. These networks also show that informal economic networks thrive among people in a tight-knit community such as a university that has people with similar needs and tastes and who have less disposal income that other segments of the society (such as working adults).