Wow, I've come across lost items.  Never a whole pack.  The most I ever found was a bundle of 4 sleeping pads and this was in Q at the NE corner of Batchewan Bay.  They were high on the rocks.  No path or trail around.  No footprints at the landing except for a raccoon.  One of the pads had been chewed on by some varmint.  The only reason for them being there I could fathom was that they had been blown there by wind & wave.

I've a bunch of pegs and guy lines that I've found on site.

Oh, I'm reminded of some gear left in APP that was appeared to be the result of a bad experience.  Not on a camping site.  Pots & pans, toiletries & a sleeping bag all out in the rain in November.  

A whole pack?  Wow.  Maybe I have OCD, but I can't leave site or a portage without one last once-over to make sure I have everything.

Again on the overall topic, it seems prudent to take 5 minutes to set up a shelter before going fishing.  Site shopping is fromage, I don't know of any experienced trippers that do it this way if at all.