I worked my way through college pretty much paying all living expenses and part of tuition with minimal help from mom and dad. The part-time experiences I found most helpful in preparing for med school were:
1) Waitressing. You make GREAT money (of course the better you are the more you make). You learn how to balance many tasks at once. PEOPLE SKILLS PEOPLE SKILLS! While it is not directly related to medicine many of the skills you pick-up will help you deal with patients and hospital staff. You learn how to deal with pressure with a smile on your face.
2) Library Copy Center Manager. This job was sooooo boring. BUT working 10-15 hours per week in a boring job...equals 10-15 hours of study time per week. No real skills learned, save how to unjam a copier, but the study time was valuable.
3) Tour Guide for my University. Again, more on the people skills and presentation skills (you will have to give many presenations in med school so this is great practice). If you are at all queasy in front of large groups this will help you overcome your fearl, because you have get these people to laugh or they aren't going to love your school.
My other experience is clinical research. This is more of a full-time position, however, many investigators have NIH grants to support a part-time coordinator. You get experience talking with patients about, at times, pretty sophisticated concepts. You also work one-on-one with physicians...can you smell LOR? To get a job like this it is important to be near a large academic hospital. Just check their job postings.
Finally, you can always be a lab tech. Not a very sexy job, and you may find it boring. Again, if you are in near a large academic hospital these jobs are a dime a dozen.
GOOD LUCK with your job search!