I would give the extra food to the humane society, weather the bag was open or not, they dont care and they so need it!
Then, I would find a food of equal or better quality that they like!
My cats are pretty picky, right now they eat Nutro Natural Choice for Kittens and they love it! At night time they also get a can of NaturaLife which they love, and is pretty good for them! My Issue with feeding my cats Nutro right now is it seems to be severely back ordered, and you can only get it at one store in town, so today when I went in to get it, they only had itty bitty tiny bags! So my location doesn't help anything! Good luck!
Oh yeah, BTW, Sharky is the resident food expert!