Regarding Souma's bento, you understand the container is made purposefully for that use and it can't leak right ?
You also understand when Souma says that the hot soup/sauce will cook the vegetables by the time you eat the bento.
Souma really did cover all of the aspects of preparing and then eating a bento several hours later.

Alice's was nice, but didn't qualify as a bento you can bring to work to eat several hours later for example.