Scan your old books and text books to see if they have a trade in value.
Use at yard sales, garage sales and thrift shops to find books to buy then trade in for income. Current textbooks can be great finds, text books can easily be worth hundreds of dollars.
Go big time and visit your local Library book sales (held a few times per year or less). Often these sales offer books for 1$ or less. Remember it must be a book that still has value, newer best sellers, more expensive books, etc. Your looking for books that have been donated to the library to raise money, not the books they took out of the Library because they don’t want them anymore.