In the car, we find that we tend to follow the same basic guidelines as when we're eating in public. Food smells linger in the small space and crumbs collect in the cracks, so we try to stick to whole fruit, small snacks, and the occasional simple sandwich. Unless we're parked somewhere, we avoid anything requiring utensils or that would take too much attention to eat.
Although you don't necessarily have to worry about other people being bothered by what you're eating, there is a potential safety risk when eating while driving. This doesn't seem to be nearly as big an issue as, say, talking on cell phones while driving, but it can be a concern none the less.
Since it's your car and your space, you have a lot more freedom to set - or break! - the rules about eating food on the go. What are your do's and don'ts?