IF you have a plan for this, and it sounds like you should, execute it. Manage by exception.
If Not. Any former active duty military on staff? As them to help orchestrate.
People first!
ORDERLY shutdown everything, then physically disco the UPSs. If staff is still on site and bugging out in their own vehicles, consider having them evac their own workstations. Your shit is already in the wind, this might save _some_ things you might otherwise miss.
The C-level officers and their secretaries PCs are important. They are not the same priority as joe shitbag in marketing. Prioritize. Printers, monitors, etc do NOT matter.
If you have one of those fancy document center (printer scanner fax wtf-ever) gizzies, and YOU HAVE TIME, rape the HD out of it. It has more juicy data than you would believe....
Servers. If you can grab em all, do so. Label EVERYTHING.
If not, grab the drives, as others have advised, and LABEL EVERYTHING. Package as well as you can. Ziplocking each drive is not a bad idea, and gives you the op to label the bag. Raid your shipping department for packing material, and when you run out, rape the padding in the office furniture.
Remember, people first!
Network infrastructure is less important than your corp data. All that being said, if you have time, now is a good time to dump the configs on the routers, firewalls, etc. to HARDCOPY to take with.
Same applies to the PBX.
Have fun....... and quit reading /. when you need to be saving your bacon!
Plan ahead next time, OK?
Red