Every day I take the train to NYC.

Sometimes I read, sometimes I sleep, but I'm always on the lookout for compelling commuter blog material. Usually I don't have to look very hard.

One recent morning, I was too tired for people-watching and slept. I'm guilty of binge-watching "The Walking Dead," and my sleep patterns have recently been significantly altered. I seem to have developed the same slack-jawed tendencies as the zombies I've watched.

I woke up five minutes before arrival. Antsy, but still sleepy, I collected my things and stood in the aisle.

A man in a nearby seat tapped my leg. "Your backpack is open," he said.

"Thanks," I replied.

I went to take the backpack off to close it, and he said, "Don't worry, I got it." He zipped it up for me.

The kindness of strangers always lightens my mood, which is high around the holidays anyway. New York City has a wonderful feeling in December. I made a mental note to pay the kindness forward.

Several seats away, a man called out, "Excuse me!" He held up a pair of gloves. "Are these yours?"

My zombie stupor got me again. "Thanks," I said. Second mental note to pay it forward.

As we made our approach into Penn Station, a woman standing in front of me looked on the floor for something. I asked if she needed help. She said, "I can't find my headphones." I found them on the floor under a nearby seat. First "pay it forward" paid in full.

Next, I got on the A train to Chambers Street to make my way to my client's office, which is near the World Trade Center. I stood next to a man traveling with his boy, about 4 years old. The little guy stood face forward, barely holding his dad's leg. Veteran subway surfers know that you don't stand facing the direction you're going, or you'll be thrown when the train jerks. Sure enough, he lost his balance and I caught him. Second "pay it forward" paid in full.

Two acts of kindness received, two performed.

I noted several things that day. 1) My karmic debits and credits were in order, 2) acts of kindness are the oil that keeps the machines of daily routine running smoothly, and 3) watching each other's backs when under attack provides the best hope of staying alive in a zombie apocalypse.

David Richman is a software program manager who blogs at thetraininvain.com.