While Rosh Hashanah can fall in October, the month of the baseball playoffs, in 1991 it fell in early September, when the regular season would still be going on. It also lasts for two days rather than just one like the episode suggests.
Eric says he locked all the bathrooms on the 747 airplane on the way flying over causing everyone to jump out of the plane. Airplane bathrooms cannot be locked from the outside.
Zach tells Mr. Sachs that he won't be at school the next day because he'll be celebrating Rosh Hashanah. Zack should have needed a note from either has parents or his Rabbi to be able to get permission to be absent from school for the Jewish Holiday.