Excellent responses above. A few more ideas:

Survey the neighbourhood:
- Have a savvy team check out the neighbourhood for better bug-in locations (restaurants) and sources of material (construction sites).

Check loading dock and mechanical rooms:
- If possible, gain access to these, for everything from tools to cardboard (primo insulation) to metal trash cans.
- The big shredded paper bin down there can be stuffed into industrial-sized trash bags for rough sleeping bags or mattresses.

Cars:
- Have people bring EVERYTHING from their cars, or at least do a complete survey. Most people have no idea what can be accomplished with a tire iron, jack, cell phone charger, booster cables, etc., let alone the other junk in the trunk.

Utilities check:
- Telephone lines may still be up, but your office PBX system may go down when the power goes off (especially after backup batts are exhausted). An old-style phone plugged into a direct fax line may get your comms up.
- Some utilities such as natural gas may still be on, but the electrical controls are off. A location like a restaurant may still have heat in the kitchen.

Power:
- UPSs for computers provide clean backup power, but the internal batts are small. Isolate your UPSs and ration them for radios and comms chargers. If you have any LED desk lamps, these will provide area lighting for a long time. Don't let some clever bozo plug in the kettle or toaster though.
- UPS batteries are typically 12VDC. In theory, you can bring in a car battery to boost your available power. In some of these the inverter may not operate without an earth ground (plugged into the outlet).
- Ideally, some of the emergency lighting should be shut off to conserve the internal battery; but that probably won't happen until too late in the emergency.

Boiling water:
- Regular steaming mugs of tea or soup will keep people hydrated and warm their body cores. Not to mention the ongoing morale boost. But how to provide this?
- Most offices don't have a simple metal pot of a useful (group) size, nor any non-electrical means to heat water.
- Many insulated carafes have stainless steel exteriors and liners. With tools, you could separate these and make tea on a shredded-monthly-invoice fire outside the loading dock.
- Of course, as an ETSer, you'll probably have a largish pot, multi-fuel stove, and gas siphon in your car. Problem solved.

As others have said, the wild card (and biggest headache) will be dealing with medical conditions with limited meds, expertise and emergency response. Offices should encourage/require people to have 72 hours of critical meds with them at all times.