The worst time to write a substitute plan is the morning you're too sick to write one clearly. The fix isn't willpower — it's building a reusable structure in advance, once, when you're not under pressure.
Separate the standing information from the daily content
A sub plan has two very different parts: things that are true every time (daily schedule, where materials are kept, fire drill procedure, which students need specific accommodations, behavior expectations) and things that change each time (today's specific lesson). Build the standing part once as a permanent folder or doc, and the only thing you need to produce on a sick morning is the daily content — a much smaller task when you're not feeling well.
Write for someone with zero context
A regular sub plan often assumes familiarity a substitute doesn't have — "continue where we left off with the reading" means nothing to someone who's never seen the reading. Write instructions as if for someone who has never been in your room: where exactly to find things, exactly what to say to start the activity, exactly what "done" looks like.
Choose activities that don't require your specific expertise
The best sub-day activities are ones that don't depend on subject-matter judgment calls the substitute isn't equipped to make — independent reading and response, a review worksheet with an answer key, a video with a guided viewing sheet. Save anything requiring real-time instructional judgment for days you're actually there.
Include a plan for early finishers and for running short
Two of the most common ways a sub day goes sideways: some students finish in ten minutes and have nothing to do, or the planned material runs out with twenty minutes left in the period. A standing "if you finish early" instruction and a backup low-prep activity (a review game, a journal prompt) prevent both from turning into unstructured time.
Leave a feedback mechanism
A simple note-taking sheet for the substitute — what worked, what students struggled with, any behavior notes — turns a sub day from a black box into useful information you can actually act on when you're back, instead of finding out secondhand from students.
Once the standing folder exists, an emergency sub plan becomes a five-minute task instead of the thing keeping you up while you're already not feeling well.