Sorry, I'm really tired and about to go to bed. I would probably just use piece instead of chunk in most situations.
You can say chunk or piece of meat.
You can say chunk or piece of iceberg.
I'd say piece/slice of cake.
You could say piece or chunk of a tree.
Garbage I'm not sure, it depends on what the garbage is, I don't think I'd say chunk.
"1 : a thick piece of something
She cut the fruit into large chunks.
chunks of meat/ice/wood/pineapple"http://learnersdictionary.com/definition/chunk
Edit: Online dictionaries only show me chunk as a noun.