The cards would feature between five and 10 items and would be written on both sides in Reagan’s inimitable shorthand.
Ronald Reagan broke the typical rule to "write only on one side" of his index cards. His cards would typically have five to ten items written out by hand.
Given some of the cards I've seen, it seems that they weren't categorized generally and with multiple ideas on the same card they also broke Gessner's other common advice.