I went to a Pulmonologist one time who told me that during his educational years, he worked as a Phlebotomist to make ends meet. That’s a smart move since he’s using a skill that he began to learn during medical school and he would know of any openings since he’s already part of the local medical system. Although I doubt it was during his time as an intern since those schedules are so brutal.
But he had several years to go after that to earn his specialty.
I would imagine that something like that is not all that uncommon since most (even part-time) jobs in the medical field are semi-skilled they certainly pay a lot better than flipping burgers. A higher hourly pay rate translates into needing to work fewer hours in their already crowded schedules.
My family doctor took a few years off prior to med school to work as a chemist for a large company before he went on to complete his medical education.
This enabled him to have the cushion of a nice little nest egg while going through the rigors of med school, being an intern and the rest of the years for his family practice residency.
Of course the lucky ones are born into families where either one or both parents are doctors. They are usually willing to subsidize their child’s education so that they can concentrate upon their studying without the distractions of financial necessity.