Another one that comes to mind for me is Joel Plaskett's show at Olympic Plaza during Sled Island in 2014. Neko Case was originally supposed to perform there that night, but unfortunately had to cancel due to some issue at the border. Plaskett was already scheduled for a gig at Flames Central later that night, but agreed to fill in for Neko as well, like the champ that he is.
A late afternoon rain storm had completely flooded the plaza, so we were all ankle deep in water by the time the band went on. Very fun night.