My first lunchbox was emblazoned with my then-hero "Zorro!" (Hopalong Cassidy was really my first hero, but he was passe by the time I entered Our Lady of Mercy Grammar School.)
I too suffered the tragic loss of the thermos bottle. I dropped the box on the playground and experienced the dread crash-tinkle-slosh described eloquently by Mr. Judge. He left out the next part, though: a cascade of milk seeping out from the edges of the box. I distinctly remember crying when I opened the box to view the disaster inside. (Thanks for bringing up a traumatic moment there, PJ)
Here's a link to a twin of my beloved Zorro box, now going for a mere $275:
https://tinyurl.com/4ucc987j