What is a collective noun for junk?

There isn't a single, universally accepted collective noun for "junk." However, you can use several options depending on the context:

General:

* Pile: A pile of junk.

* Heap: A heap of junk.

* Mass: A mass of junk.

* Collection: A collection of junk.

* Assortment: An assortment of junk.

* Mischmash: A mishmash of junk.

More specific:

* Junk yard: A junk yard full of junk.

* Dumpster: A dumpster overflowing with junk.

* Clutter: A house filled with clutter (can refer to junk).

Ultimately, the best option depends on the specific situation and the tone you want to convey.