Unfortunately, I'm in circumstances very similar to those you describe. Probably worse. Typically more than 30 miles from my vehicle, and in a building where I face the possibility of having to go through metal detectors and having anything I carry x-rayed, they nonetheless encourage you to have a "go-kit", implicitly if not explicitly for evacuation after a terrorist attack.

Those who have been on this forum awhile can imagine how I feel about not even having a pocket knife for those circumstances.

Anyway, I've devoted a lot of thought to it, and probably more money than you want to devote to these kits, but you might want to consider that such an evacuation can happen any time of year, in any weather. In a large event, people might have to go some distance on foot... one of the things we learned from 9/11 is that you want to KEEP GOING, not stick around to watch the drama unfold, to try to hail a cab, or to take "shelter" under a handy awning. You want to keep putting distance between you and the "action" by any means available.

One of my first thoughts would be a poncho of some sort- even a disposable one (if not too terribly fragile) would be very welcome in some circumstances. It may not provide much insulation in the cold, but there's no quicker way to hypothermia than being both wet and cold.

I also carry a fleece cap, a fleece neck gaitor, and a flat-folding pair of ear warmers in the winter, and a rolled-up canvas brimmed hat in the summer. I don't know how much you're willing to invest, but none of those items cost a lot. Keeping the head warm in winter and cool in summer is half the battle, and gear to do that is much more compact and effective (per weight and bulk) than the equivalent gear to do the same for the rest of the body.