As an improvised toilet if flushing water or sewage disposal are not available.
The sawdust soaks up liquids, and the charcoal reduces bad smells.
Store used buckets outside until the thaw and then bury or compost the contents.
If you have a woodstove then the ashes from this are useful for the same purpose.

Many of the small macerator/lift pumps used to get sewage into raised-bed drainage fields for single-family homes are quite small. Most are under half a horsepower. Combined with a small reserve storage capacity in the pump chamber and drain lines and it should be possible to run the pump off a simple inverter connected to a vehicle a couple times a day.

You could run the well the same way. Running the well off an inverter you could store water and get as much heavy use done as possible. Then switching over to the septic system you clear the lines.

It would take a bit of coordination and handiness with electrical equipment but it isn't that complicated. Easier still if when the well and septic pumps were installed the installation incorporated the extra equipment that makes external connections easy. Something to ask your contractor about.

MY home is set up so that critical systems have backups - when the power goes out, I don't have an automatic transfer, but I go out, start the generator, plug in the cord (I use a portable genset and rigged up an underground feed back to the house from the shed), go to the basement, flip a few switches and I have water, septic, furnace, fridge, freezer, some lighting and a microwave all up and running. It's a small generator (3,500 watts/220v) so I do have to balance loads a little, so I tend to leave the furnace OFF and run the woodstove instead, and we have electric hot water, which takes 100% of the generator to operate, so we leave that off the backup.

So it's not ME. It's the residents who don't have that kind of setup that I'm planning for. One of the other things we learned from this incident study was that people who abandoned their homes to stay with friends/family found out the hard way that their baseboard heating systems (water filled) and other pipes froze and burst while they were out of their homes. So another part of the drill is if they are going to evacuate, we need to remind them to drain their systems out - and even then, they need to check J and P traps and other low spots in their plumbing systems for cracked pipes.

Most of the training I get for this position borders on "duh" but this scenario is very close to home, we've had ice storms, and we will have ice storms again, so we're really thinking it out.

Next up for the incident command training sessions is one that I also don't like to think about, because it's also in the realm of very possible in my district - we have an annual fireman's carnival.

Here's the scenario description:

"Your small community is having a carnival. On the grounds of the carnival are rides, vendors, a mercantile exhibit, a stage with musical performances, food tents and so on.
On site you have one BLS ambulance with a crew of two, two state police troopers and one fire engine from the local volunteer fire company, but it is not fully staffed.
There are approximately 1,500 people at the carnival.
It is a cloudy evening, and the weather forecast is calling for isolated storms.
From cloudy but not stormy skies, a bolt of lightning hits the ferris wheel, and the resulting power surge knocks out the main generator for the carnival rides and starts several small fires in the food tents.

What is your plan of action?"

Yikes. That's just so incredibly possible for us...

In a well designed and built system both supply and drains, excepting the traps of course, drain dry once the caps are removed. In very cold locations it sometimes pays to invest in some drain antifreeze, typically propylene glycol as it is non-toxic. A splash down each drain protects the traps and avoids the unpleasantness of finding out a trap, even worse the toilet, froze and cracked.