Okay, so you come across an apparently abandoned pack.

Your role is that of a concerned citizen. If somebody is hurt or lost, you are potentially the first link in the chain of rescue.

But it may also have been abandoned by mistake or circumstances you cannot know (sudden snowstorm, change of route). People do all sorts of crazy things.

You will check around for a little while, but probably do not have the time or ability to do a thorough search of the area.

It is appropriate to check the pack for indications of the owner. Do not remove anything, or dig in too deep. But it is appropriate to check it and leave it as you found it. Make a note of what you find. If there is ID or medication, this is important as an indication that someone may be in trouble. Some backpacks have zip-off daypacks, so look for that. If there appears to be spoiled food or damage from animals, note that as well; it helps establish a timeframe of events.

Obviously, if you see any indication of foul play, you leave everything alone.

Leave the pack with a note giving an approximate timeframe when authorities will be notified. It would take some pretty extreme indications to abort a multi-day trip, but you go with your best judgement. And you do report location and gathered information to the authorities.

You do not, ever, remove the pack from its location. Not only does that put you on dicey legal ground, it may put someone in jeopardy.