Once you are finished with a class, sell the books you have purchased. Provided they are in good condition, your books can be sold back to the school book store or to a fellow college student. If you are not having luck finding a buyer, visit an online auction website and list the books there. When you ship college books they can be sent by "media mail" through the United States Postal Service; this is cheaper than first-class mail.
Advertise on community websites and around the college or university that you are available for odd jobs. Ideas include tutoring (if you are particularly good in a subject), baby-sitting, dog-walking, moving furniture, painting and landscaping. Think about what odd job you would enjoy doing the most, as well as how much each will pay. For instance, tutoring may be more lucrative by the hour than baby-sitting. Create an advertisement that includes a contact email address or phone number and post it anywhere you can obtain permission to do so. Fit the odd jobs in around your class schedule.
While many people know about donating blood to organizations such as the Red Cross, you can also donate blood to other medical offices and science labs that reduce donations to blood plasma. These blood plasma visits will pay you for the donation. Ensure the facility is registered with your state health board. Also, ensure the technician is using items that have been fully sterilized or are out of freshly opened packages.
As you move away from childhood and into adulthood, you may find that you do not need many toys or possessions you had growing up. Look for items that are light to ship, or are of significant value. For instance, jewelry, gift cards, video games, name-brand clothing and accessories such as leather jackets, boots, wallets and purses are all suggestions. Access an auction website and list the items. Use the United States Postal Service's Priority Mail Flat Rate package packaging to ship the items.