I agree with the ‘find a way to eat when not in the car’ sentiment if that’s possible. After reading this thread, I tried hard to think of healthy (and safe) car friendly food and came up with very little.
Slightly off topic, but I drive 100 miles / day and got myself into the habit of buying a minimum of 2 packs of mini cheddars (and sometimes other stuff too) when filling up with fuel. Clearing out the junk from the car typically involved a covert operation to sneak all the evidence into the bin. No idea who I thought I was kidding - I must have added 800-1000 calories every time I filled up. These days, the car is littered with empty water bottles instead !