Over the years I have driven off several bears by making noise both in populated campgrounds and in the backcountry. Some could not be scared off.

From the SIBBG website:

If a bear enters your area:

* Check to make sure all your food and food-related items are stored properly.
* Get everyone together (especially kids) and look really big and make lots of noise (e.g., yelling, banging pots, clapping, etc.).
* Never surround a bear--they need an escape route!
* Never separate a sow from her cubs (sometimes cubs are up a nearby tree).
* If a bear huffs at you and shows its profile, it may be ready to bluff charge. Stand your ground or back away slowly. Do not run.
* Never try to take food back from a bear!