Managers at In-n-Out make 40-60k, I heard. Their cooks start at $8/hr! 😀
OP, as mentioned before, DON'T overextend yourself! I worked full-time while going to grad school full-time. Then I took science prereqs and started slow, but did the same full-time school sched for 2 semswhile working a demanding job . The first sem, I did well. The second sem, I started volunteering in a research lab on top of everything. I did okay, but had two B's. I guess getting B's are okay given that I had a busy schedule, but i kept kicking myself cause I knew I could have done better if I had more time to study. Plus, I was tired all the time, my husband missed me, chores weren't done, and my dog hated me for being gone all day and not playing with her. I spent all of winter break trying to unwind because I was so wound up - I couldn't relax, and I kept sleeping at 3am even if I didn't have anything else to do, since I was so used to it. Also, I almost fainted when I saw that I got a C in BioII, which ended up to be an error. I told myself I would never forgive myself for getting a C simply because I overextended myself. So this sem I decided to take the paycut (ouch) and lose my benefits and my "title" for a lower, more flexible position with half the hours. I'm glad I did, now I'm stressing less and have more time to study.
Moral of the story, if you feel overwhelmed, cut back on work or on school. Focus on getting good grades. Your GPA and your MCAT scores are the first thing adcoms look at. Hope this helps.