A lot of games have special things that happen for holidays. This would be especially easy for Uru, as Earth holidays are completely IC. Here are some ideas for specific holidays. Italics indicates additional ideas that would be harder to obtain. Cleft 2.0 should probably be read beforehand. Feel free to add more ideas.
Chinese Lunar New Year
Red Chinese lanterns are set up in the 'hoods, and Zandi hangs one from his trailer (you know, the cheap kind you can find in supermarkets). If you approach Zandi, he gives you a red envelope. Instead of money, it has a Relto page for red Chinese lanterns in Relto. While you can only get the red envelope on Lunar New Year, the Relto page can be turned on and off at any time. Zandi could also say "gung hay fat choi" in a self-conscious accent.
4th of July (Independence Day in the U.S.)
Zandi flies an American flag from his trailer. That night, there are distant firework displays that can be seen (and heard) from the Cleft. If we do get somebody to do more voice acting for Zandi, and do have Zandi telling stories, he could tell some inspirational story about Pres. Lincoln or something.
The World Cup
A soccer ball appears in the Cleft for a day. Maybe in a few other Ages as well.
As in more things for Christmas. Zandi's storytime could have a special set of Christmas stories that he'd tell during this time of the year.
Maybe some fireworks.