I missed this article when Kim posted it, but I'd like to suggest that those who replied are missing a fundamental point: you have to prepare for two scenarios here, not one. The first is what if you are in close proximity to and directly affected by the incident; the second is what if you aren't. The events of 7/7 are still fresh in my mind.
With regard to the first, you simply need to survive to get yourself into the hands of the emergency services ASAP. Multitool, whistle, torch, mask, and water are a bare minimum here. I like the idea of the goggles but I think a ski visor would be better, simply because it's easier to put on - less likely to get tangled in something else - and more comfortable. Let the emergency services take care of you after that.
With regard to the second, while you still may need those items from the first scenario, home may not be reachable, but mass transit will only be stopped for a day or two. People often commute long distances, so having friends nearby who can put you up is good. At a pinch, sleep at the office. People should also be aware of secondary functions of items. When you can't make a telephone call, texting may still work. My phone will operate as a radio, so I'll be able to hear news broadcasts.
With regard to the water, freeze it! It will keep you cool in the hot tube as it melts.