Depends on where you backpack. Here in the Sierra, the marmots are super aggressive and WILL chew up a pack for the salt on the straps.

I do not worry about humans taking my pack. First, my pack is old and does not look very valuable. Second, most backpackers are already carrying all they want to. Third, my pack is black - not easy to see. Just camp away from the trail and you are not likely to have any problems.

My pack oubles as a day pack so I do not have to worry about it in camp since it always goes with me.

Personally, if I were worried about human theft, I simply would not backpack in that area.