Nikki, I am a decorative painter/faux finisher which means I can have a pretty crazy schedule. Some days I am home all day, but others I need to be at a client's house by 8 or so and I like to work strait through (time is $). I usually won't leave until 6 p.m. or so. I have a client I am starting 1/29 and her house is 40 miles away - so add the commute and you are talking about a long day.
For days like this, I know it will require a supreme amount of pre-planning to stay OP. I will create mini meals that I can pack in my trusty cooler (not too big) and either eat cold fare or ask if I can use their micro (most clients are cool with that). Then, when I get home I'll probably only need a light snack. I know it seems like a ton of work and really inconvenient, but I keep thinking of the alternatives - continuing to do manual labor with an extra 60+ lbs. on me, climbing scaffolding at my size, etc.
Trust me, it is worth the commitment to pack it up the night before. Also, is it possible you could buy some dinner alternatives near work - salads from Subway (then you only have to carry dressing)? Try to map out some healthy alternatives on your route between school and work where you can pick up a chicken breast or something that works.
Hope this helps. I wish it were easier but I suppose if it were we'd all be waifish little things