Danny gives a good answer. The character in this book is not using proper english. He uses a lot of slang and poor grammar, as someone from that time period, region of the country, upbringing would use. What he is saying in the passage is: We don't have waste our time in a bar. Other people might be sent to jail and no one would care. But that isn't the way it is for us.

The previous sentence in this passage adds a bit of context to the beginning. The whole section reads: "With us it ain't like that. We got a future. We got somebody to talk to that gives a damn about us. We don't have to sit in no bar room blowin' in our jack jus' because we got no place else to go. If them other guys gets in jail they can rot for all anybody gives a damn. But not us." The double-negative "don't have to [x] in no [y]" is a regional slang typically associated with southern parts of the USA. It just means "don't have to", in this case "don't have to sit in a bar". "Blowin' in our jack" I believe means talking into their drinks (jack = Jack Daniels whiskey maybe?), being another slang term for talking with nobody listening to you. "If them" is the same as "if they", but again it's a regional slang. "Rot" in this context means "To rot in jail"; to spend the rest of one's life in prison, literally to rot like fruit. "For all anybody gives a damn" means that if the previous statement were to be true (in this case, "If them other guys gets in jail") then nobody would care about it. All together this sentence can be read as "If those other guys went to jail, they could spend the rest of their lives in there and nobody would care."