Didn't hear it in this trailer. In what context the phrase was uttered? Was somebody trying to smoke a cigarette and just wanted a dry match?

nah...not when somebody wants a cigarette :)
I was trying to find that clip, let me search again now...still searching...

Finally, I could not come up with that exact clip and have not found the movie script, but, I found a news article talking about that specific phrase. And, Now I realized it's probably the bitter "humor" the playwright wants to set in the story.

In the movie, the "match dry" appeared on different occasions. They are all literal meaning except for the part which I wondered about.

The medical doctor was giving a seminar on how destructive and damaging the artillery to a soldier's body/life. Then the doctor asked Dunne in front of audience, something like, what is the worst thing for an soldier in the war?

Dunne was a little distracted and had some gruesome flashbacks. Then he responded with "couldn't keep the match dry"? Then audience chuckled and the doctor felt a little embarrassed. And, I got lost...

Now seems I found the answer in the article below. I don't know...

Quote****The film recreates the horrors of war by juxtaposing gut-wrenching battle scenes, a melodramatic romance and domestic upheavals back on the Alberta home front.


Only one scene ­— Dunne thrusts a bayonet into a young German soldier's skull — is a faithful recreation of his grandfather's experiences. But everything in the movie was inspired by the real Dunne, Gross says.


"To be honest with you, it's probably pretty hard for me to pull that all apart now....There was just lots of stuff of his that just stayed with me and showed up in a variety of ways. I did ask him: 'What was the worst thing about the war?' And he did say: 'You couldn't keep your matches dry!' I have also read that, so it is echoed elsewhere."


That reference is used in Passchendaele in a scene that seems comic, and then becomes poignant.


"That's not farce," Gross says. "I think that life got quite reduced and your creature comforts were very, very small. And they all smoked. We don't smoke enough in the film, honestly."

*******End Quote, from
http://www.thesudburystar.com/ArticleDisplay.aspx?archive=true&e=1282852

There you go. It's hard for soldiers to retell the horror of war. When cornered by a psychiatrist, an innocuous mishap like not being able to keep the matches dry seems to cause the least amount of long lasting psychological damage. And yet that's probably the defensive mechanism of the human mind taking over - self-deprecating humor plus treading the water lightly.

After all this psychobabble it may seem an oxymoron, but don't read into it too deeply. ;-) It just means what it means.