Collect books from the trash or anywhere else you can find them and sell them to used book stores. The bigger chains like Barnes and Noble pay well for used books, particularly textbooks that are still current.
Give blood to make some extra money. You can't do this all the time but giving blood is a quick easy way to earn a few dollars. Just be sure that you are medically able to donate before exploring this option.
Be a guinea pig for science. Scientific studies need people to test their trail medications. Some of these studies pay well. Investigate any program and the company offering the program. Some of the experiments may have side effects.
Write Internet content online from home. Many Internet content generating companies will allow you to put that education to use writing content for various websites. This is also a good option because it offers you the flexibility of working around your school schedule.
Become a tutor. If you are particularly skilled in a certain academic curricula, you can put up an advertisement on campus and in the newspaper offering your services.
Sell your hair. If you have long, healthy hair, there are wig companies that will pay good money for your tresses. You can't do this often, but every little bit helps.
Complete papers and essays for other students. Students are often willing to pay for good schoolwork. If you develop a reputation for excellent work, you can get a decent client list.