You asked whether best to travel in front or rear of the train. Seems to me (I'm speculating, and could be totally wrong) that riding in a rear car, if given a choice, would be advisable. In the event of a collision, or encounter with something placed on the tracks, might some of the impact energy be dissipated towards rear of the train?

Reading accounts of several past subway mishaps, looks like deaths are frequently fire-related. In the worst subway disaster (1995, Azerbaijan): "Many of the 300 deaths were caused by carbon monoxide poisoning when toxic materials (vinyl and plastic seat cushions) in the subway cars caught fire."

Despite your opposition to carrying a "gas mask" (can't say I blame you), why not consider one of the small emergency smoke hoods. If you're convinced there's a high likelihood of an incident, and you're serious about making reasonable preparations, something to think about.

This one, for example, claims 20+ minutes of carbon monoxide, toxic gas and smoke protection, and carry size is only 5-in. x 3-in. x 3-in. and weighs 12 oz.

I see the Montreal subway system characterized as "the world's most extensive system of interconnected pedestrian and Metro subway networks...linking buildings...." This being the case, do you carry a small, but accurate map of the system (or at least the section you travel) to help locate escape routes?

I second the recommendation to upgrade the light source you carry. Dense smoke would challenge a keychain light. Maybe something like a small 1- or 3-watt LED flashlight, and a spare battery. One example: my 3-watt Nuwai QIII takes one 3-volt lithium battery, puts out lots of light, and is just 3-1/2-inches long.

Does each subway car have its own emergency equipment (tool for breaking out glass, first aid kit etc) on board? If so, knowing where it's located, and what it contains, would be essential knowledge.

Finally, given the complexity of the underground maze, I wonder if a small compass, used with your map of the system, would be of any use (or might underground minerals make inoperable)?

Good luck with your quest.

Dan