If you are planning to use that to climb out of a window, better get some practice in first. You may find it's impractical without a full abseiling harness.

It sounds like you are looking to get out of the building, and then home. I'd add a whistle, a dust-mask (or N95) and a bandanna. And that's about it, really. You may need clothing to walk home, but if you walked in then presumably you already have it. Presumably you know the local area pretty well.

Your employer ought to have medical kits. You might consider volunteering to be the first-aid guy, or fire marshal, or similar, to help check they are doing it right, that the supplies aren't all past their expiry date etc.

In a situation like that, realistically you have to consider other people. For example, it might be worth getting a load of cheap coin-cell lights so that you aren't the only one with a torch. Stuff like that (and the tire iron) you can probably leave in your desk, rather than carry it in and out every day in your backpack.