I used to do lunches for my flatmate, who also worked on the road.

He had a cooler bag. I thought along the lines of picnic for him. Mini quiches, baps (flat breadrolls) - with various filings, I used to get the small baps and make up 3 or 4 of them for the day - basically they were no rounder than the palm of my hand - so a good variety and easy to eat. Crudets (carrots, corgette, celery, cucumber) with various dips. Home made cakes/slices/biscuits (Sunday was baking day). Trail-mix (usually home made). Coffee, sugar plus long-life milk. Also for drinks, I'd get small iced coffees, juices etc and freeze (or semi-freeze) them - to help keep the food cool longer and by the time they've melted they're wanted.

If there is enough room in your DH's car, then maybe get one of those mini fridge/coolers that go into the lighter source. You could get more adventurous then.