Safe from what exactly?
People...my guess most folks have too much of their own stuff to haul your pack back it them. With that said, I would not leave any expensive electronics in them to tempt fate.
Marmots...This is your basic "do as I say, not as I do" thingy. Don't leave food in your pack and leave the zippers open. I've left food in a canister inside a pack at Lower Trail Crest numerous times with all the zippers zipped up and have had zero problems.
