For several days before launch astronauts and cosmonauts are quarantined to ensure they don’t get sick with a cold or another communicable disease during their flight.
Astronauts and cosmonauts have superstition based traditions that trace back to the first people to fly in space.
For cosmonauts, that would be Yuri Gagarin. As Yuri walked to his rocket, the chief engineer gave him a smack on the rear end. That practice is still followed. Yuri also took a leak on the tires of the bus that took him out there. That tradition is still followed (by male cosmonauts and astronauts).
Another tradition for cosmonauts, although it doesn’t go back to Yuri, is to watch the film White Sun of the Desert the night before launch. Another more recent tradition is that a Russian Orthodox priest will bless the crew with water.
For NASA astronauts, the traditions go back to Alan Shepard. Alan had scrambled eggs and steak for breakfast, the day of his flight, so most astronauts do today.