I mean, it's quite obvious when something is special or more expensive.
There's usual groceries and then something different not from the usual store or its something that looks more expensive, a treat, special etc etc etc
I've been married 10 years and it really isn't any effort not to eat all/the last of something that we aren't sure if the other person wants.
It really is just basic politeness when living with other humans and I think especially as women, we fall into the trap of micromanaging and feeling the burden of "tell him everything or else it's not his fault".
Nope, I expect my husband to have eyeballs and to stop and check if in doubt.
As for "if it's there its to be eaten"... sure, but to finish or take ALL of something is inconsiderate
And no, we don't have permanent leftovers because it takes less than 5 seconds to say/text "hey, do you mind if I eat that last cupcake?".
The other person always says "no problem" or maybe "sure, but can you save me half".
It stops that disappointment of looking forward to something and then feeling deflated.
On the occasions we HAVE finished something or eaten all of something, we make the effort to replace it so the other person can experience the same joy or enjoyment we did.
You don't have to do this, but literally everyone I know tends to do this to varying degrees.
As with anything, I suppose it varies depending on your family and friends.