Face... Have you tried putting it into a zip-loch bag after it's opened? (Typically a gallon zip-loch - minus the Nessie - and drop the cereal bag bagandall into it. 'Family sized' cereal boxes require a two gallon zip-loch, but I doubt you are buying it in that quantity... ;-)) The zip-loch seals tighter than re-wrapping the interior 'cellophane' bag, and putting the cereal in its bag into the baggie adds another layer of seal...
Of course, it still won't last forever but it will stay edible after opening for a longer period...
My problem is that some things, I just don’t eat often enough to warrant buying a big box. I would be better served with cold cereal to buy the “variety packs” and freeze them until I wanted one. Otherwise, the whole thing will go bad, as what has happened now.
I live in an area where food storage is common, and buying in bulk is the norm, rather than the exception. The freezer is just 5.6 cu ft, so I try to make small packages, especially meats. I’m still buying for a family of four and that’s hard to break out of!
I WILL learn how to do this!! Thanks, NC. I appreciate your suggestions. I never even thought of variety packs until I read your post about the cereal. My brems dun fel owt.