One thing about train derailments (or big fires in industrial areas) is knowing which way the prevailing wind blows. Some of these train chemical leaks and fires unleash a deadly toxic stew that kill within seconds or minutes if breathed in.

If at all possible, you don't want to be downwind of the derailment or fire and you certainly don't want to head in that direction if under an evac.

Aside from the masks that others have mentioned, a typical urban centric BOB should suffice and will allow you to live out of house at a hotel or family/friends home for the duration of the evac which could vary from hours to weeks.

Typically these urban BOB kits should contain personal hygiene products, essential meds, OTC meds, a couple of changes of clothes which includes work clothes if required.

In addition to our BOB kits, we have a medium sized, dedicated bathroom bag that contains new toothbrushes, toothpaste, general OTC meds, deodorant, shampoo, razors, makeup (not for me!) TP, towels, washcloths and so on. The reason for this bag is so that if we ever have to do a hasty evac to a family or friends home for any duration, we won't have to go out and purchase many of these items or be a burden on our hosts to supply us with.