True, it would be a very bad idea to have a part-time job.
Think about medical school as an investment in paving the path to your future career. Working 10 hours a week at $15 an hour would make you an extra $7500 per year for your first two years of medical school, but that's time you're not spending studying for class, boards, or keeping sane and maintaining relationships/health/sleep. You are transitioning from a land of more-time-than-money into the land of more-money-than-time. That $7500 is chump change compared to the income differences you will yield by placing into a top residency that sets you up for whatever you want to do - academics, fellowship, working in a highly desirable location. Time you spend churning out work is time you're skimping on the other demands of your life, particularly your "other" job - studying to be a doctor.
As a second year, I only know a few people who do Kaplan or self-scheduled online tutoring, and a few who might do some freelance work if they have journalism/art skills when they have time. No one has a "real" part-time job, as far as I know. I personally babysit 1-4 hours a week for fun money - I don't even count it as income when budgeting. It's like a little bonus that means I have to withdraw from the ATM less often.
Your loans will pay for everything you need. Don't worry. It takes time to adjust to the idea of obligatorily being in a large amount of debt (remember - unless you fail or quit, you _will_ pay it off and come out on top.) And yes, the big negative six-digit number is still going to be hanging over your head whether you make some side-money during med school or not.
EDIT: I take it you are in high school? There are a ton more pre-med school-related topics in the High School and Pre-Allo forums that you might find more helpful than this one. I bet it's something on a lot of people's minds.