Here in California, anything that can not be stored in the refrigerator or out of sight in cupboards in the TM needs to go in metal "bear box" if there is one at the campsite. Most National Parks (Sequoia/Kings Canyon and Yosemite) around here have them; National Forests may not. In Sequoia this summer, since we ate mostly outdoors, it was most convenient to keep most of the food in the bear box, but we had some food inside the TM as well. I just follow whatever "bear aware" advice/rules that the campground advises. We (with our kids) have observed many a black bear from a safe distance and talked about bear safety, food storage, human impact on their environment, etc.
Unattended cars, however, are a different matter here in California. Cars with coolers or things that look like coolers or cars with food scents do get damaged by black bears from time to time. Backpackers also need to take precautions.
In areas where Grizzly bears live, somewhat more caution is needed should you encounter one. However, considering how many people visit Yellowstone NP where both Black Bears and Grizzly's live the following NPS link should put things into perspective:
http://www.nps.gov/yell/nature/anima...per/info1.html
Kevin