I would have the boss stay in charge if I could and then just act as his advisor and maybe his adjutant.
This solves a few political problems.
Since the boss is responsible for the building it is easier to tell people to do stuff to it if it is under the bosses authority.
Once the chain of command is clarified comes the next steps.

Comms' list of things to get is pretty good.

Inventory of the situation and supplies is first.

I am going to assume the office has a fairly large crew and might even occupy their own building
If it doesn't it might be helpful to see who else is in the building. If there is more than one office unit occupying the same structure you will likely want to work together.

Then you need the supplies inventory
This includes whatever is in stores and whatever is in people's cars. Count everything from spare clothing to coffee filters.


If there happens to be a working radio then a radio listening group and a news reporter will help. People like to be informed.

Since an office and a blizzard are in the scenario you could send a detail out to collect snow. It can be melted for flushing toilets or if it is cold enough that the plumbing is frozen it can be melted for kitchen use. Snow is pretty clean usually but I would still have a crew boiling it.

Maybe some people could be kept busy clearing snow from around any cars in the lot too.

Like Comms mentions, nothing hurts moral more than somebody feeling bored and useless, so one of the things that would really help is having something for everybody to do.
That could include a group to do entertainment if your office is large enough.
Once the basics are attended to might be a good time to practice an office choir sing-along or something.
Maybe the group could do a bit of theatre, or somebody might even be a musician.