I think I ‘outgrew’ mine and by 5th grade, was also brownbagging it.
I served in the Air Force with a guy who would bring a “Muppet Baby” lunch box during week-long “Local Salty Nation” exercises. On the last day of each exercise he would whack it with the edge of his helmet to make a “hash-mark” denoting another exercise over.
Ahhhhhhhh, the memories...
A small file’s “notch” on the lid’s lip, would have worked nicely, too.