I kept seeing this poster & t-shirt from Raygun, the greatest store in the universe (they say so themself!) & thinking, huh, how about that, a Midwest expression I never heard of. And then, I heard myself say it. And then I noticed that I say it ALL THE TIME. Ope, forgot the bag. Ope sorry. All the ways they say people use it, I do too. That was totally weird. It's innocuous, not a word as much as a breath, so I totally see how I never noticed. I suppose everyone I know has been ope'ing my whole life & none of ever noticed.
On a different but related topic, in Norwegian it's grammatical & common to say, for example, "I'm going to the store - do you want to come with"? omitting "me" or "us" at the end. When that came up in my Norwegian class a while back, one or two of us instantly recognized it as a midwestern pattern. I only ever noticed it I do it when people on the east coast called it out. I had no idea why we did that & it was cool to see a Scandinavian pattern carried into English.
It's hard to catch yourself in a regional expression unless someone else hears it & reflects it back to you. That's part of why I so much appreciate studying the beautiful Norwegian language.