How to pack food for a hike?

Planning to hike through Yosemite's Misty trail and want to know if there's a proper way to pack my food when hiking through bear country. I'll have a backpack to keep my lunch in as I am sure the hike will be a few hours. Do I need to pack it in strong enough bags that the scent won't escape and attract bears? Or do I even have to worry about that at all?