What to do if you run across a Bear
Even if you have no food out whatsoever, you may still encounter a black bear wandering during its daily travels. Upon spotting a human, the naturally curious black bear will either a) run away, or b) stop and observe the human.
If you want to completely avoid black bears, talk continuously or make loud, unnatural noise (i.e. Bear Bells). This will scare off most black bears.
If a black bear DOES come uncomfortably close, or if it starts approaching you, back away SLOWLY, always watching the bear. Speak in a LOUD, DEEP voice (It doesn't matter what you say. I use "GO AWAY BEAR" as it also serves to inform others around me of my situation).
What to do if you have a Black Bear in Camp
If you can stand being scared a bit, and you have taken good precautions to hang anything that smells out of their reach (and keep a clean tent and site) just let them be. They'll probably wander off in a bit. If not, you can try to scare them off by making a loud, deep noise, or bang a shoe against a pot. That'll probably scare them off. If the bear tries to rip through your tent (it does have sharp claws), back towards the door and leave (or go through a wall if you must), talking to it LOUD and DEEP (try "THERE IS A BEAR IN MY TENT. I AM NOW LEAVING" or whatever else comes to mind). You should be trying to inform any public around of your situation. DO NOT turn your back to the bear. Try to make yourself as TALL as possible. If it attacks (***VERY UNLIKELY***) be the aggressor. Fight back vigorously.
But remember: you are in black bear country. The black bear is completely entitled to wander wherever it wants to, and if that includes your site then so be it. The black bear did NOT come to your site to try to attack you, it is just naturally curious. It smelt something different, maybe your food, and just wanted to find out what it was. The black bear does NOT want to fight.
Don't Run
DO NOT RUN AWAY FROM A BLACK BEAR. THEY CAN RUN FASTER THAN YOU.
Do Not Play Dead With a Black Bear
(Editor's note: Black bears eat carrion (dead things)). It is curious, and will rip you open just to see "what's inside"!