There really isn't anything that will hold food and drink from the door or steering wheel that could be used to eat while driving.
It's possible you could find or make a floor console with a dropped top to place next to his seat on the right side. The dropped top should be set in from the edges so the food won't fall off the console.
I would also limit the types of meals he eats while driving to those he can easily pick up and put down (think fast food restaurant food - nothing requiring a plate, fork, spoon, or knife).