What can a engineering student do in free time to earn some part time money?

I know that a engineering doesn't have free time to do any thing else, even the life of an engineer is like an employee of a marketing business who doesn't have time for his girl friend. But here I am giving some options that can an engineering student do while studying without spoiling his/her study. And also this will not affect exam results, even supply or back or re holders can do these jobs.