If you go to Yosemite, they require you to use their bear boxes, including while you've parked during the day. At least you don't have to pay for them, just keep unloading and loading the car (which, of course, gets old very fast!). At the entrance station they had on display a car which a bear had ripped open as though it were a tin can--those bears must have extra tough claws to rip metal like that. I'm just glad those bears don't live up here in the Pacific NW! (Ours are quite shy, for the most part.)

I hope that list helps you find what you're looking for!