Keep On Truckin' History & Origins
The phrase Keep on truckin’ had its genesis in ancient history - depression era pre World War II , that's pretty ancient. A song entitled “Truckin’ My Blues Away” by Blind Boy Fuller in 1936 is the earliest mention of the phrase in pop culture. Fuller kicked the bucket in 1941, but probably turned in his grave a few times when the unkempt, unbathed hippies of the 60s and 70s adopted his creation as a pop slogan.CLICK TO VIEW -IT'S MADE FOR YOU
The phrase didn't jump right out of Fullers song and fall into the Hippies laps, it had a lot of help from an underground cartoonist.
Cartoonist R. Crumb [Robert Dennis Crumb], an avid blues aficionado  picked up on the phrase and adapted it to a one page cartoon which appeared in the maiden issue of an underground publication Zap Comix . It depicts a series of comical men strutting across various landscapes while toting the phrase “keep on truckin’” - needless to say it was a hit.
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The phrase became a slogan of the 1960 counter culture which din't sit well with Crumb. Even though he himself was an "underground" artist. he had a dislike for the Hippie culture and considered it pretty 'crumby' that they would pirate his work, he somewhat disowned the comic. He refused to allow it to be licensed and became incensed over its use in advertising and on various products launching several lawsuits in the ensuing years. 
I became acutely self-conscious about what I was doing. Was I now a ‘spokesman’ for the hippies or what? ... Keep on Truckin is the curse of my life. This stupid little cartoon caught on hugely. … I didn't want to turn into a greeting card artist for the counter-culture!
He was offered, like, millions to license the 'Keep on Truckin' drawing for Toyota, but they only wanted that one drawing. He wanted to sell them a lot of other stuff.... he turned them down. - Terry Zwigoff 
Various adapatations of the phrase have been used in Rock Music by groups such as the Greatful Dead 
1. That Crumb heard the phrase and adapted it is pretty much established, although he himself has never admitted as much. He did publish R. Crumb's Heroes of Blues, Jazz & Country which is readily available to this day.
2. Zap Comix: an underground comix series which was originally part of the youth counterculture of the late 1960s. While a few small-circulation self-published satirical comic books had been printed prior to this, Zap became the model for the "comix" movement that snowballed after its release. The title itself published 17 issues over a period of 46 years. - Wikipedia
4. The court ruled that because Crumb didn’t place a copyright notice on the page that the work was public domain. The ruling was later overturned and Crumb retained the copyright for the art.
5. Grateful Dead song Truckin: Mr. Natural had a bunch of sayings. One of them was ‘Keep on Truckin’,’ which was the spirit of our song. : Bob Weir Gives Fascinating Backstory on How “Truckin’” Came to Be Thanks to the Dead’s Travels