My favorite was a record single included with an issue that played a song but played with a differently every time (well up to eight times). Super Spectacular Day.
This is done by having multiple concentric grooves in the record. When you drop your needle on, it'll play one of the grooves which makes it seem randomly selected. Another example is Monty Python's Matching Tie and Handkerchief, which has two grooves on one side to make a "3-sided" record.
