Interview day activities will vary widely from program to program. They might include a presentation (prepared ahead), case presentation (developed on site or ahead), group interviews, 1:1 interviews, etc, etc.
Each site should let you know if there is something you need to prepare ahead of time (e.g. presentation).
Otherwise you should practice interview questions, think about examples from rotations/other situations to support your candidacy, generate questions you want to make sure you get answered during your interviews, etc.
I spoke to one residency coordinator from a site that required presentations ... she said they were always a bit annoyed when the topic of the presentation wasn't relevant to the site (e.g. peds presentation for a hospital that doesn't have a peds unit for example).
Its a small thing but usually there is a tour involved (a looong tour in large hospitals) so wear comfortable dress shoes (especially important for the ladies).
I spoke to one residency coordinator from a site that required presentations ... she said they were always a bit annoyed when the topic of the presentation wasn't relevant to the site (e.g. peds presentation for a hospital that doesn't have a peds unit for example).