At least in Western Canada, dumpster diving has become impossible: all major chains now have fully enclosed dumpsters that attach to the side of the building, and can only be accessed from inside the building. Plus, most of these are compactor units, which crush the contents down into the dumpster portion that gets hauled away.

I would hope that they would be able to forecast demand reasonably well and use any extra for other products that might sell better in between holidays, like cold cuts, before it gets stuffed and packaged up only to end up in the dumpster.