After clearing the base game, I've moved on to the Undead Nightmare DLC.
I've noticed that money seems to be all but gone from the game as a commodity. Nobody seems interested in trading now that zombies ate their neighbors. Further, the challenges are completely different than in the base game. However, I can still collect animal parts and plant bits.
It seems that the spawn rate for herb patches is vastly increased - I wish I'd had this many to choose from when doing the challenges in the base game! There doesn't seem much point to collecting plants, though. I can't make Tonic, and I haven't found any shops willing to buy my supplies.
Similarly, instead of skinning animals, I can take a large amount of bits from them instead - sometimes I get ~10 bits of animal from looting a single corpse. Again, nobody seems interested in these animal bits, so I'm not sure if it's worth it to collect them.
What good are plants vs zombies? Should I collect animal parts, or are animal corpses better left for dead? Are these wilderness-resident goods evil? Are there any use for these items in Undead Nightmare?