Dineral is a colloquial and emphatic way to say "a lot of money" or "a fortune." It's more vivid than simply saying "mucho dinero."
In the context of "El Centenario," it highlights the protagonist's success in the drug trade, as he "regresa con un dineral" (returns with a fortune) from his trips to Los Angeles. This word perfectly captures the theme of wealth and illicit gain central to the song's narrative.
This song, "El Centenario (En Vivo)" by Betillo Guerrero featuring Legión RG, tells a story about someone who chose a different path to escape poverty. It starts by pointing out a harsh truth: "Si eres pobre te humilla la gente, seré rico te trata muy bien" [If you are poor, people humiliate you; if you are rich, they treat you very well]. This friend got into the mafia because they were tired of being poor. Now, they have "dinero de eso por costales" [money by the sackful] and everything is different for them. They drive a new car and are no longer looked down upon.
Even though the government is after him ("lo persigue el gobierno"), he keeps working, traveling to Los Angeles often and returning with a lot of money. The lyrics mention that he's gotten used to danger and travels through places like Tijuana, Culiacán, Los Angeles, San Francisco, and Las Vegas. It takes a lot of courage for this life, because "no se permite ningún error" [no mistakes are allowed], and he's always dealing with the law or his boss.