The Waste Lands provides examples of the following tropes:
After the End: In this book the results of the collapse of the Great Old Ones' civilization are made apparent in the eponymous Waste Lands. When looking at the horrific landscape and the nausea-inducing creatures that live there, Eddie is dumbstruck:
"This was no nuclear war," Eddie said. "This...this..." His thin, horrified voice sounded like that of a child. "NOPE," Blaine agreed. "IT WAS A LOT WORSE THAN THAT, AND IT'S NOT OVER YET."
A.I. Is a Crapshoot: Shardik, Blaine, and Patricia all went crazy years before the start of the series.
Dangerous Key Fumble: Jake has to go through a Haunted House to reach a magical doorway that will take him to the others in Mid-World. Just as the house comes alive and tries to eat him, he drops the key that will let him open the portal and it falls through the floorboards.
Gasher: Why not? Give me a chunk of broken glass and I'll rip it right off and stick it right in, for all the good it's doing me these days.
It Tastes Like Feet: Eddie asks Roland if billy-bumblers make good eating. Roland answers no, they're horrible: tough and gamy, and he'd sooner eat dog. When quizzed, he confirms that, yes, he's also eaten dog meat.
Living Lie Detector: Blaine can determine if someone is lying with 97% accuracy by using voice analysis.
Madness Mantra: "SEE YOU LATER, ALLIGATOR. AFTER A WHILE, CROCODILE. DON'T FORGET TO WRITE"
Meaningful Name: The city of Lud, whose surface inhabitants have forgotten what technology is and now fear it. At one point near the end, the point is made explicit when they are referred to as Luddites.
Mordor: The titular Waste Lands, a vast area beyond the city of Lud which Roland and his ka-tet must cross with Blaine's dubious help.
Wasteland Elder: Eddie daydreams about meeting some of these ("wise fuckin' elves!", he muses), who would give the ka-tet some food and supplies and maybe tell them the best route to the Dark Tower, when he sees the Lud skyline from a distance. He realizes, though, that the chances of them meeting anyone like that are slim to none (though they do meet some decent folk in River Crossing).