I think that memories of Kennedy campaigning at Dubrow's might win for the memory most commonly reported by people who have contacted me through this blog. It makes sense - it was clearly a big deal, and as these pictures show, hundreds or perhaps thousands of people showed up.
Edit: I found this article in Sheepshead Bites that has a nice description of one person's memory of Kennedy campaigning in front of Dubrow's. It also confirms what my sense was - Kennedy's assassination was one of the most defining event for Baby Boomers, and so many of them have also retained closely their memories of him as president and campaigning to become president.
"My singular Kennedy experience was when the senator, after winning the Democratic nomination, campaigned in Brooklyn, in the summer of 1960, for New York’s 45 electoral votes. My friend Larry and I went to the rally along Kings Highway that stretched from Ocean Avenue to Coney Island Avenue, and onto several side streets, and waited hours among the jam-packed crowd. As we stood at the East 16th Street intersection, opposite Dubrow’s cafeteria, we were constantly pushed and shoved by others impatiently awaiting the candidate’s motorcade."
(Neil Friedman, Nov 23, 2013, retrieved from http://www.sheepsheadbites.com/2013/11/jfk-assassination-remains-a-defining-moment-for-baby-boomers/)