It just plain grates on my brain to hear or see "a couple ______". Come on. Using "of" is no formality -- it is just good basic sense.

"I went to the store and bought a couple apples."

Really? I know Gala apples, and Fuji apples . . . Never heard of Couple Apples -- and do you buy just one, I am unclear.

"I want to clear up a couple things."

Hm. I'm not your significant -- in fact, I hardly know you -- isn't it premature to start discussing "couple things"?