Dunno about the nineteenth. But it was a hobo song of the 'teens (20th Century). In that period "regular" was frequently used to simply mean praisworthy, acceptable, worhty of trust; and a "combination" was any series of engine and cars as I recall. It was common to buy tickets taking changes at various nexii to take a local branch line to get where you were going, but a Cannonball being an express train would not stop until it got to its destination, a major terminus, and no changes could be taken.

The above is my own interpretation and not authoritative.

A