Truth. My not-so-secret-secret (aka what everyone does) is to initiate a scene based on a premise/something everyone laughed at during the opening. So far, it’s been working.
Enjoy it so you remember it like you remember your favorite movie/tv show?
I don’t know. Just do it. Remember stuff or don’t do improv.
What I realized about remembering in general, whether ideas from the opening, or even what the beats in a Harold were, is that it’s easier to remember things that are good. If your opening is just a bunch of random words, or the same idea rehashed over and over again, or you didn’t establish something close to a Game in your first beats, then you’re going to have trouble remembering. A good idea is easy to remember because your brain can succinctly label it. “Grandma likes cats more than kids” is better and more memorable than “those crazy old ladies who have a bunch of cats and spend all their money on them.” Maybe.