DD is only 7 months old, but so far she has had bottles and once "solid" food in the car on road trips. We did a 4 hour (without stops) trip when she was 2.5 months, and got pumped BM and formula in bottles while DH drove. At 5.5 months, we drove 7 hours (again, without stops, with stops it was closer to 9) twice. I was lazy about pumping at that point, so bottles of pure formula, and one meal of baby food was offered but she was too hungry and impatient so she didn't even eat it. This was when I started to suspect a formula intolerance/allergy - one bottle, she ate slightly more than half of what I expected, rejected the rest, then a few minutes later threw up the whole bottle. She was sitting in a small lake in her carseat until we could pull over and clean her up, ewww. DH cleaned up DD and the lake, and then we put a plastic grocery bag over the wet carseat cover so DD wouldn't get all wet and nasty as soon as we put her back in. Luckily it stayed in the carseat, and didn't go through to the vehicle seat below.
Since DD is still so young, we don't really have car food rules for her yet. It will probably be something between what I was raised with, and what DH was raised with. DH was raised with no food/drink in a vehicle, ever. I was raised with food and drinks in the car on road trips only. Nothing messier than crumbs food-wise, and pop (soda, cola, carbonated beverage, whatever you want to call it).