In the flashback of Lily stealing six pack, we can hear the song "500 Miles" from Marshall's Fierro, which is a running gag since the second season.
The Cat Stevens song The Wind that was played at the end was also used in many episodes of the TV show This is Us. Mandy Moore who played the girl that got Ted to get the tramp stamp would later be on This is Us playing Rebecca Malone Pearson.
The security guard that shocks Barney would later go in to play Sheldon's father in Young Sheldon.