I stopped by my local Steak N Shake for lunch today. And needless to say, they're really smart.
Their to-go container for the fries fits in your cup holder! (Much like the one seen here, however from Steak N Shake, not Krystal.) It stands upright on its own, and is PERFECT for being in the car.
So if you're ever on the road and in search of fast food, don't overlook SnS. Not only is their fry container perfect, the fries are DELICIOUS!