It may be obvious. At least, if you have often flown.
First comes those silly questions at the ticket counter. "Did you pack your own bag? Has anyone else had access to your bag?" As if someone up to no good is going to tell them. Even if you aren't up to something, will you tell them? If The Old Goat's wife packed his bag, he's still going to say, "I packed it myself and nobody else even breathed on it". After all, wouldn't you be afraid of what they might put you through if you answered yes to those questions?
Then you sit in the boarding area and those announcements come over the speaker systems every few minutes, "Don't leave you bags unattended."
The Old Goat was flying in or out of Denver, either heading out or coming home, he doesn't remember. It was crowded. Some one's baby was crying. They announced first class could board and anyone needing assistance could board. He was in coach, waiting the call for his seat's row. The announcement came over the speaker, "please don't leave your bags unattended."
That's what he though of when he wrote the poem.