Those 'boxes' is what gives the bumper lower structural rigidity, and also play an important aerodynamic role, especially at speed. The middle one directs airflow from the hot radiators below the car. They're not expensive, especially the side ones (about $24, I think), but the middle one is about $140, if I remember correctly. Ask Tischer.
As for not hitting them, you need to approach the driveway sideways. Also remember that's easier to hit those parts going down than up, so exiting your driveway backwards is another option. Good luck.