I drive around all day for my job so the thing I fight most with is eating in the car and when I eat in the car it's always crap from convenience stores. I have tried to bring food from home but I always stop when I don't have time one day or whatever. Plus whatever I bring isn't what I am craving so...
I drive around all day as part of my job too, but I don't seem to have this craving for something in the car with me. Perhaps a good start would be to get fast food that's at least a little better for you?
I have been going to Taco Bell at ordering off the Fresco menu which is not that unhealthy. Now I need to stop getting crap from the convenience store on the way home. I have stopped doing this before I just seem to start again.
Personally, I'm completely addicted to the Swiss Oatmeal at Corner Bakery. It has some sugar in it, but the oatmeal fills me up for much of the day. For lunch type foods, it sounds cliche but I'll stop at Subway for a relatively low-calorie sandwich (I just can't stand the "Subway smell").