Instead of something elaborate that's taking the place of the thing you want to remember, how about writing a sticky note with "remember the umbrella" on it?
Yeah ops method seems strangely elaborate. I do something similar but require far less to actually jolt my memory. Usually I just put a shoe upside down on my table, takes a couple of seconds and in the morning I think "Why did I do that? Oh yeah, thats right", has never failed me yet.
Or just use built in memory. If something is worth remembering then remember it, simple. I do not consider diaries that vital or to-do lists as being anything more than long term storage. It is not the same as knowing what you should be doing that day. For that built in memory does nicely as does having details at hand on a phone.
Regarding the umbrella, if I forgot it then I would be pleased with my brain for filtering that useless requirement out.
In a thread about remembering little things, you're actually advocating that forgetting them is good?
I used an umbrella on my way to work last week. I forgot to bring it home. I was sad because it was raining the next day, too. I was not pleased with my brain for filtering out that arguably useful requirement.
