When the gang visits the mall, a sign proclaims it is 246 days until Christmas. Assuming the film's events take place in the year of its release, the date is April 23rd, 1974. However, Easter fell on April 14 in 1974.
According to Charles M. Schulz, the bunnies that Snoopy dances with are the Bunny-Wunnys, the characters from Snoopy's favorite children's book series.
Had Snoopy, as the Easter Beagle, thrown just one less egg on the ground when he first arrived, he would've had an egg for Charlie Brown.
The song that the music boxes play (and which Peppermint Patty, Marcie, and Snoopy dance to) in the second scene in the mall is a classical piece written by Johann Sebastian Bach and entitled "Minuet from the Anna Magdalena Notebook (BWV Anh. 116.)."
The jig playing in the background when Snoopy arrives as the Easter Beagle is the first movement of Beethoven's 7th Symphony in A Major. The second movement from this same symphony is heard when Sally turns impatient about the Easter Beagle's appearance.