I graduated from university before hiring out. I agree that you need time to live. Go to a few good parties at school, drink beer, and get laid. I decided to follow my interest in railroading, since I couldn't see sitting in an office for the next 40 years. The difference was that I came from a railroad family, and knew what I was taking on.
Both career paths take lots of sacrifice. Bachelor degree, medical school, and residency are all hard to get through. The benefit is a lucrative, and in demand career. The railroad doesn't take so much school, but it might take some time to get year round employment. Sometimes they over hire, based on the number of guys, who will reach retirement age. Sometimes these guys might decide not to go, due to personal reasons. Governor Christie may cut Transit's budget.
With this in mind, it would be advisable to have a backup skill set. I have my degree, a CDL, and food service experience. You may need this, even if you don't get cut. If you screw up, you get suspended.
On the other hand, part time work is hard to hold. As a young employee, you will be a spare, as mentioned. Sometimes, like summer vacation season will see you working lots. Best to save up, since there will be lean times too. You need to bridge the lean times, by living like a camel, who conserves water, since he doesn't know when he'll find more.
One more point is automation. Who knows when technology will advance to that point. You can't know if it will be here by 2069, when you would be eligible to retire. You know that we will always need doctors. Why not join a museum? That way you can cut people open all week, and play choo choo, on the weekend? If you do occupational medicine, you might be able to do the railroad, and medicine. We have a doctor, who heads our medical department. She deals with our fitness for duty, and advises us on good nutrition, and sleep habits. I lost hearing in one ear. The doctor got me special equipment, so I could still continue.