We all keep our rituals. Many people have gone back to religion for a bit of stability - there is a theocracy city state in the Southeast somewhere, I'm told. Others have their own little celebrations. We mark the day of The Event, or our birthday, or Darwin's Birthday, or when they first survived a reanimate attack. Everyone needs a holiday, and while supplies don't allow for great feasts very often, even if its for a non-nonsensical reason like Pi day, people look for an excuse to make the occasional splurge.
I tend to recognize the first of May. We're all working now - no more stock options, no more desk jobs - so Labor Day seems like a good choice.
Sometimes, its not a day, but a time, or an act. More than a few people have become obsessive about disassembling a certain piece of equipment, or checking every centimeter of a rope first thing in the morning, or last thing at night. Makes sense - your life might rely on that thing some day - though unscrewing it too many times is probably going to damage or loosen something.
Verbal tics seem to be common too. Either people refuse to say good bye - disliking the finality of such statements in dangerous times, or go the other route and always presume their fare-wells will be the last ones. A few have become brutally honest - what is the point of lying to dead men, and aren't we all dead here? Others have given up on honesty, preferring the comfort of their own little worlds.
There are quite a few people who see the Zone as a new frontier, or a shot at freedom and fame. Really, its just a mad house, and we're all crazy.