I save tons of pesach food from yr to yr.. i have learnt that shoprite sells their food with 50% or more OFF during chol hamoed. All is kept well in a bug free closet. i have never had problems.. and i check. sometimes oil or matza meal for that matter has a little smell from being old.. so i save those packets for frying not baking.
and besides, do you really know whether the groceries are saving their stuff yr to yr? what do they do when pesach is over? certianly don’t throw it all out..