When I was there, I remember alot of bear sightings near the campgrounds. And I mean grizzly bears, not black bears. I dont know if I would venture backcountry with food anyway. The backcountry fee is 4 dollars.
As far as camping, it gets cold (near freezing) every night, even in the summer. There are 10 major campgrounds and numerous backcountry sites. These campgounds normally fill before noon in July and August. This is a good site link:
http://www.glacier.national-park.com/