Symbol Analysis
No, we're not talking about a festival where folks get dressed up in elaborate costumes like their favorite fantasy and sci-fi characters. That kind of convention became popular long after Whitman moved on down his own road of life. In this sense, "convention" means doing what's expected, what's traditional, what's "normal."
You should approach that last word with extreme caution, says our speaker. What's "normal" to some may be a total waste of time to others. The poem's use of conventional imagery is related to the idea of appearances. There's something more to life than our day-to-day grind. All you have to do to experience it is to step out on the open road.
For example, the speaker wants his travelers to know that true wisdom is waiting out there. It's "not finally tested in schools;/ Wisdom cannot be pass'd from one having it, to another not having it;/ Wisdom is of the Soul" (78-80). Laters for all that schooling nonsense, he argues. To get to the wisdom of the Soul, you have to undertake a voyage, just as the Soul is doing.
Be warned, though. Folks might laugh at you: "You shall be treated to the ironical smiles and mockings of those who remain behind you" (148). These squares just can't see past the conventional reality of their daily lives, though. The true traveler is unconstrained by any social expectations: "What beckonings of love you receive, you shall only answer with passionate kisses of parting,/ You shall not allow the hold of those who spread their reach'd hands toward you" (149-150).
In other words, traveler, you're just going to be you. No amount of convention is going to break your stride; nobody's gonna slow you down.