Wow. I think there was another recent thread about things that flabbergast you, and this is one of them.
I can see not liking milk at all, or carefully making sure the milk and cereal are gone at the same time, or putting in more cereal, or drinking the leftover milk.
But I would not have believed that so many people see nothing wrong with throwing it away.
I usually throw in more cereal until most of the milk is gone, then toss the small amount left over after that (it’s usually a very small amount–I’ve been known to put in more cereal more than once if necessary).
I’ve started putting kefir on my cereal in lieu of milk. It sticks better to the cereal so there’s none at the bottom, which is an improvement, and I love the taste (probably not for everyone though). Before that I definitely drank the milk left over (though I didn’t leave much).
I would never give the leftover milk to a cat though - cow’s milk makes them sick, especially with bits of cereal in it. At least mine. Maybe your cats have iron stomachs, but mine can’t keep it down when they manage to eat anything not strictly on their diets!
I once did a sleep over with a friend in the 5th grade. We had rice krispies the next morning. They don’t soak up much milk. I politely drank my excess milk with a spoon. He had about a third bowlful of milk. His mom just put the bowl in the fridge. I asked him about it later and he said she’d give him cereal with it the next morning.
I guess that makes sense for people that aren’t fond of milk. Just reuse the milk with more cereal the next day.