First, and most obviously, GET A JOB! A job is the most reliable source of income for most people. even minimum wage could be enough to support a good lifestyle in college, when coupled with grants, scholarships and possibly loans.
But if job hunting is leaving you empty-handed, what then?
Well, if you're proficient in a subject, become a tutor! Tutors can often easily make $10-20 an hour, if not more.
If you're not so proficient in any subjects (or not good enough to help others with it) you can always sell things you have lying around online, on sites like craigslist or ebay.
And if you run out of material things to sell, your body makes a wonderful thing called BLOOD PLASMA, and you can sell it at biological centers all over the place. The place near my campus will buy a pint of your blood for $15 to start, and will offer an addition $5 each visit. So, the first time you get $15, the second you get $20, the third time $30, and it continues at this rate up to $35 a session. Sounds great for someone who is willing to give up their blood, doesn't it?! The only issue I've encountered is that the supply for plasma is much greater than the demand. You might need to wait outside the doors on a monday morning if you want to get in for your first session. Getting your foot in the door is the hardest part!