Holidays will be active for a very long time. Even though many people will become non-religious, it does not mean that people want to stop special celebrations.
Halloween, a holiday dating back for a few hundred years, and most likely a few more centuries to come. Children will still enjoy going from house to house, but costumes will most likely be replaced with realistic holographic effects and some temporary DNA altering. Future Halloween will have scarily realistic holograms for decorations. Plastic masks will be banned for concerns about children with asthma.
Christmas will continue to exist, but not as a religious event. Many children will still beleive in Santa. Families will get together and presents will be exchanged at the snowy white ground, because global warming would be eradicated before it can effect much. That's because nanobots will neutralize all the pollution in our land, air, and water by the year 2025.
Although people will stop thinking about Jesus Christ as a superhuman diety, children will always love to collect easter eggs and eat chocolate. That will be a traditional that will never be stopped but become healthier with soy replacing milk chocolate. Presents will also be bought for younger children at Easter but they will be the latest in hyper virtual reality video games.