Can't carry a gun to school or the office? Feel defenseless? What are you gonna do about it?
As always, be aware of your surroundings—look at the fire-escape plans. There should be a bunch of maps posted all over the place, and they will show the fastest and most direct way out of the building in case of fire (or active shooter). As long as that route does not take you toward gunfire, you should be OK. At some point, however, you need to check those routes to make sure they are current and recent renovations have not altered the building's layout.
Think about the fire alarms—would it help or hurt to pull the alarm as soon as you see an active-shooter or other workplace-violence incident? That may be a good way to let everybody know they need to get out of the building.
Look around the office or classroom. Can the windows be opened? If not, stash a good-sized hammer or hatchet in your desk drawer. You can use it to break the windows and/or to defend yourself. What about the resulting jagged glass? Rake the hammer along the sides and bottom of the window frame, then throw a heavy rug or thick coat over the sill.
"But I am on the second floor!" Quit whining. Invest in a flexible escape ladder, attach it to a piece of 1.5-inch heavy-walled metal pipe that extends at least a foot on either side of the window and voila! Instant escape (after you break the window).
Going to someone else's building for a meeting and feel that walking into their conference room with a Louisville Slugger or a framing hammer may not be the best first impression? Look for the fire extinguishers, heavy printers, copiers, shredders, sturdy chairs—anything that can be used as either a weapon or to break a window and facilitate escape.
The bottom line is we may not always be allowed to have our trusty firearm with us, so you have to use your head and some imagination to come up with a plan to stay alive.