Normally you would just say "keys" in most contexts. i.e. "I'm looking for my keys" "There are lots of keys on my keyring" "My keys are locked in my car"

a bunch of keys = a lot of keys, perhaps 10 or more. a set of keys = best choice! a couple of keys = two keys.

Thank you Daniel .

The only time I have ever heard "a couple of keys" used is in that song: "Flying into Los Angeles Bringing in a couple of keys..." But they were referring to a different kind of key.