Reselling textbooks — This is a great way to bring in some money. When you’re done with a textbook, see how much it’s going for online. You can even compare that price to what the booksellers on and around campus are offering, and see which one gets you the best deal. (Buying used textbooks online is also a great way to keep more money in your pocket each semester!)
Parents have a natural inclination for tutors who have studies from the same the same school as their child's. You can use this to your advantage if you are living with your parents. Alternatively, you can register yourself for giving tuitions online and find interested people. You can also teach things to your peers or juniors at college and charge them money for it. Keep your rates lower than professional tutors so that students see an advantage in studying from you.
I surprisingly get a lot of people asking to detail their car. I never intend to make a business of it, but I love doing it to my cars and people ask me to do it to theirs. All it takes is a cheap orbital buffer (mines a used craftsman) and a shop vac. I normally get easily $100 for a basic wash/wax/vac, or $200 to remove scratches and polish then wax the car.

Apply for new scholarships and grants. A lot of students think that they are only eligible for funding when they initially apply for admission. This is a mistake! There are often new scholarship opportunities for upperclassmen, though they aren't always widely advertised. You may also be able to apply for external scholarships or grants, which are offered from groups outside of your school.