A classmate cut hair (which was almost certainly illegal, in retrospect...). Easy gig, and he had all the business he wanted right there in the dorms.
Heard rumors that someone would buy a car at each break, drive it out to school, and flip for a profit. His angle was that the cars were salvage titled imports that had been rebuilt, and his home state allowed title washing, or something like that. I think the DOT closed the loophole that he was exploiting.
I did put out three pieces of shareware, but never saw a dime from them.
The biggest move I saw were my Pakistani roommates. They and all their friends brought back one duty-free "prayer" rug every time they went home. They could make about $2,000 on each rug.
I did know one student who used a cash-back credit card to pay other student's tuitions. He'd split the cash-back with you, but his real benefit was bumping up his credit rating.