Emergency Plans - Not So Easy

I’m sitting on this side of the Christmas school holiday, and somehow it seems shorter than it did at the beginning – always does, I guess. Now I must tackle the work that I promised to do over the break…emergency plans.
Now, this might sound simple, but it requires a great deal of thought. As a virtual teacher, there are no supply teachers who are trained to do what I do. There is no one who can step in, read over my lesson plans and carry-on as usually with just a few extra discipline problems.
If I am to be absent from class, I must pre-teach the lessons and record them. This is analogous to standing in front of an empty classroom and teaching to the video camera. When the students come into the digital classroom, I will not be there (they are, of course supervised at their end, but instruction comes from my end). They will be able to view the archived lessons that I have left for them. To continue the analogy, they will press “play” to watch the video of the lesson I made for them.
This situation is clearly far from ideal. What if the students have questions that I have not addressed? What about the interactive nature of the class? Where there are multiple students at a similar level, I can allow some time in the lesson for discussion amongst themselves (either by asking them to pause the lesson, or allowing it to play silently until I begin speaking again). Where a single student is involved in a lesson, I can pause for reflection time before sharing my own thoughts, allowing a semblance of conversation. This is an imperfect system, but is none-the-less a workable one for the occasional teacher absence. After all, we can’t always count on the quality of the lessons completed by conventional substitute teachers either.
A planned absence for a day is one thing, I simply record my lesson the previous afternoon based on where the students need to go next. It is like teaching an extra day, but it can be worth it for a really good workshop. What about an unplanned absence, illness for example, which would prevent the pre-recording? What if the unplanned absence spreads over 2-3 days? My colleague quite suddenly lost her voice for 3 days in December and was unable to teach. School could not be canceled? What to do?
And so we come to the emergency plan. I am to prepare a short unit to fill about 3 days of instruction and work time for my students. It should be appropriate for any time in the year (I can clearly not do an extra day’s teaching each week!). Ideally, it should be appropriate for multiple grade levels (we could use it next year too!).
So here I sit, searching for the “ah-ha” moment as the holiday minutes tick away. Anybody out there have a ready-made lesson for 3 days of project-based instruction for students in a variety of grade levels that requires not particular background knowledge? It should be relevant and engaging and of course make appropriate use of the time to cover important elements of the curriculum.
I’m coming up empty.