Think small. The more compact the burger and the fewer toppings, the less it drips or disintegrates.
Don't try to hold a hot drink between your knees. If your car doesn't have a cup-holder, don't buy coffee or hot chocolate.
Avoid anything that requires a knife and fork.
Avoid clubs and sub sandwiches.
Remember the three magic words: "Hold the sauce."
There's no such thing as a dainty dipper. You've got to take your eyes off the road to aim for the dip, and it's a long, drippy way to your mouth. The little container can fly all over the car if you make a sharp turn. If you insist on dipping, park the sauce container in your ashtray.
Wraps can work for or against you, depending on whether they're loosely flopped around a filling or tightly folded to prevent leaks.
Processed "American" cheese, used in most burgers, can melt into a glue that holds the lettuce, tomato and onion together. Not so for melted mozzarella on pizza it stretches like third-graders at a taffy pull, taking a lot of sauce with it.
Avoid trough-size drinks. They don't fit in a standard cup-holder, and you can't get your hand around them for a firm grip. A refillable handled mug is easier to handle on the road (most drive-through staff will fill your mug instead of a cup, on request).
If possible, leave on the wrapper of a sandwich, burrito or burger, to catch the drips and crumbs. Unfold it as you bite your way down to the bottom.
Resist the urge to turn your head sideways to get a better bite of something. The result could be a surprise lane change.
Stock extra napkins in your glove compartment.
If you get a nasty food spill and can't change your clothes, put your top on backward when you get to your destination (this obviously doesn't work for button-down shirts.)
Ask to have big burgers cut in half so they're more manageable.
Look for restaurants that serve whole-leaf lettuce rather than shredded, which tends to fall out of burgers and tacos.