A six-panel comic by Robert Crumb in Zap #1 (1967) named after "an old song and dance from the mid-thirties that came out of black culture." For almost a decade, this slogan and its strangely-ambulating pronouncers (see below) were nigh-ubiquitous, stubbornly sticking in "the collective hip unconscious" and appearing on countless items of merchandising, the vast majority of which were unlicensed.

That changed in the early '70s, when Crumb's lawyer threatened lawsuits against anyone who had used Crumb's work or ideas without permission. Phat loot rolled in, but in 1976 a judge ruled that Crumb didn't own Keep On Truckin' after all and the IRS got (and stayed) on his back forever, for taxes they said he owed on past royalties which the judge had said weren't even his.

The "Keep On Truckin'" pose is difficult to execute in Earth's gravity to non-comics characters, but for the home viewers foolish enough to try themselves, we will describe it:

    Lock the left leg in a fully-extended position, as though you were standing at attention.
    Keep the left foot firm at a 90 degree angle to the leg and, using your right leg bent out and behind you for support, lower yourself to a 45 degree angle from the ground, which you rest on with the heel of the left leg.
    The torso and head should continue the line described by the left leg, with the top of the left arm running straight down along the torso and the forearm sticking out at a 90 degree angle straight in front of the torso.
    The top of the right arm should jut in back parallel to the ground, with the forearm dangling straight down.
    If you haven't fallen over yet, this is the opportunity for you to flop your long nasal proboscis down over the front of your suit jacket.

Oh, you were hoping for an explanation of the text rather than the context? ... that is, what the words actually mean in that particular arrangement? The easy answer is for me to say "Whaddaya want? This phenomenon predates my birth by over a decade - ask someone who was alive then!" but the objective answer isn't likely to be much more informative: though this came before Crumb's legendary batch of bad acid, it's become a little nugget of pop culture, famous only because it's famous like "Where's the beef?" and "I've fallen, and I can't get up!" I could say "you had to be there," but the truth of the matter is that a lot of people who -were- there still didn't get it. (In Simpsons episode 7F14, "Bart's Dog Gets An F", Marge Simpson is called upon to explain to Lisa what her "Keep On Truckin'" patch on the Bouvier family quilt means: "I didn't know then and I don't know now.")