There's the beginning of the airport scene in THE MOST CRUCIAL GAME, which is like some mini documentary about the place. In fact the VISUAL side of the WHOLE scene is like that. It would have a completely light feeling to it, it if weren't for that wounded veteran you see at one point.

Couple of good ones. - When he gets stopped by traffic enforcement and his car is inspected.
When he is told he had to take his pistol test by the sergeant and captain and then internal affairs.
When he pulled over for reckless driving and is escorted to crime scene by motorcycle cop.

And to me the best, ultimate non essential scene is the one with the funeral director on the steps of the funeral home in Swan Song. Scotti and Falk do such a great job in it, and I think Falk had to stop himself from laughing. The scene has nothing to do with the solving the murder, Columbo is only waiting to talk to the victims brother. I'd say when the writers wrote it they had in mind the way Falk and Scotti would handle it or that it was not in the original script but written later when Scotti became available.

Good ones..! I don't recall the Swan Song scene I'll have to re-watch that episode.. :-) Any other 'donations' gratefully received..!

There's another scene in Swan Song that's not essential but makes me smile every time. When Columbo and Luke are standing by the table waiting for Tommy Brown to finish singing his song so they can talk to him, a little scene plays out like this:

Columbo looks at the food and says "This smells good."

Luke: "Help yourself."

Columbo: "Are you sure? I skipped breakfast this morning."

Luke: "It's fine. Help yourself."

Columbo lifts the lid and asks: "What's this?"

Luke: "Chili."

Columbo takes a bowl, takes a bite and says: "This is good, I've never had chili that tastes like this."

Luke: "That's a special recipe made out of squirrel meat. Dat's good ain't it?"

Columbo, putting the bowl down: "That explains it."

It's a short 30 second scene, not essential to the plot, but I smile every time I see it.