In Chapter 10 of Part 2, Sal is lonely and delirious with hunger. While roaming the streets, he has a transcendental experience that he describes with similes.
I realized that I had died and been reborn numberless times but just didn't remember especially because the transitions from life to death and back to life are so ghostly easy, a magical action for naught, like falling asleep and waking up again a million times [...] I realized it was only because of the stability of the intrinsic Mind that these ripples of birth and death took place, like the action of wind on a sheet of pure, serene, mirror-like water. I felt sweet, swinging bliss, like a big shot of heroin in the mainline vein [...]
Kerouac often characterized On the Road as a novel about a spiritual search for meaning, and he was insistent that his Catholicism drove this search. He would also, like Allen Ginsberg (Carlo Marx), learn about Buddhism, although Buddhist leaders didn't always think the two men got the belief system right. Regardless, this passage is an excellent example of the spirituality present in On the Road. Bodily deprivation has led Sal to a transcendent state, and it leads him to "realize" several things about the nature of his soul, including that it has been reborn "numberless times." With a simile, he compares the easy, forgettable process of reincarnation to "falling asleep and waking up."
He then speaks of the "intrinsic Mind," a unifying life force that he says powers the cycle of death and rebirth. This concept is far from original to him, but the Beats played a large part in introducing these ideas to the United States. The 1960s counterculture movement would also invest in the idea of a unifying life force, which writer Aldous Huxley called the "Mind at Large." To explain this concept to readers, Kerouac metaphorically says life and death are ripples across the intrinsic Mind, then expands on that with a simile: reincarnation is to the intrinsic Mind what wind is to a sheet of water. The ripples move across the surface, but they do not change any inherent properties of that surface.
Finally, Sal says he "felt sweet, swinging bliss," an alliterative and metaphorical description of his elevated mood. He expands on this with a simile that compares the sensation to "a big shot of heroin in the mainline vein." Kerouac tried, but was never addicted to, opioids like heroin, but many of his friends, including William Burroughs (Old Bull Lee) were lifetime users, and recreational opioid use is still associated with the Beat Movement.
In Chapter 11 of Part 3, Sal's descriptions of his travels become melancholy. This tone is communicated with a simile in which Sal compares himself to a traveling salesman who sells something no one wants to buy.
In the misty night we crossed Toledo and went onward across old Ohio. I realized I was beginning to cross and recross towns in America as though I were a traveling salesman—raggedy travelings, bad stock, rotten beans in the bottom of my bag of tricks, nobody buying.
First, note the alliteration in the phrase "old Ohio." After his usual brief descriptions of the places he crosses through, Sal reflects with some displeasure that he's only retreading the same ground as before. In a simile, he compares himself to a traveling salesman, and not a successful one: he says the kind of salesman he's similar to is "raggedy," with "bad stock" that won't sell. The "rotten beans" comment may be an allusion to the story of Jack and the Beanstalk, in which Jack buys magic beans that his mother thinks are a hoax. What is Sal selling, and why isn't anyone interested? Perhaps he worries in this passage that his attempts to find purpose and spiritual meaning are pointless "tricks" that are obviously rotten to everyone but him.