For whatever reason, when I say that to Kyra and Luca, it seems to have more meaning than the translation alone. Perhaps it's a bit of nostalgia thrown in with wishing my family a good day, even if they don't have a lunchbox.
Note: The comic above is copyright Bill Watterson 1996. It can be found on p. 15 of the Calvin and Hobbes collection, "It's A Magical World" (on Amazon). Reference: Calvin and Hobbes Strip Search.