Here's a few tricks my coworkers and I used to use when working on the gas pipeline - it would be continuous work when we installed mains with inspectors on sight so we found ways to sneak meals in...
Fill a decent-sized shaker cup with one cup of regular ol' instant Quaker Oats and then dump two scoops of protein in it. If water isn't available, make sure to have two bottles with you for each of these shaker cups.
Dump water in, shake up real good, let it sit for a minute or so, shake again, chug as fast as possible.
This gives you close to 60g of carbs and protein with little fat. If you want healthy fats, keep a small jar of peanut butter in the cooler and use some fast food spoons to eat a scoop or two.
Make sure to rinse that damn cup out or your kitchen will smell like ass until the dishwasher is done running.
Homemade sandwiches are your friend as well in these cases. I could inhale a sandwich from the time it took to grab a tool from the work truck and walk back to the job site. Always make sure you have something work-related in your hand so it doesn't look like a lunch break - you're just utilizing your time. If you toss a sandwich and a shaker in your daily routine you're good money. Sometimes I would make half sandwiches and eat them every two hours - easier to crush in minimal time and, with sandwiches, you can easily manipulate macros. Wheat bread, overloaded with deli meat, lettuce, tomato, low-fat cheese, etc.
If you're stopping for gas somewhere or to use the restroom, you can always get some milk and use that in a shaker with protein in a pinch. Or dump the protein in the milk container and shake. Carbs from the milk can replace the oats. We would go half on a bag of protein and a big tub of oats from your favorite wholesale grocer from time to time just to look out. Only do the milk thing in the Winter, though. Get some Dollar Store, plastic measuring cups to put in the oatmeal container if you're keeping the supplies on the truck. Otherwise, just dump your stuff in the shaker before work and bring with you ready to mix with bottled water.
Vanilla protein in a Gatorade was done by some but I couldn't stomach it on the regular.
Drinking a bottle of water an hour is a must, maybe two if it's a heat advisory day or there's no shade. Gatorade is essential for cramping when it's wild hot outside because of electrolyte replacement.
None of this shit is optimal, but it does work.
Two shaker cups and a sandwich and you're potentially looking at 120-150g of both carbs and protein. Sometimes better than most of us eat on the weekend when we can cook all our shit. Minimal cooler space needed for this also. Warm or room temperature water even works better with the shaker - cold water doesn't mix as well.
Hope this helps a bit!