I've only shot a shotgun match a couple times, but, you'll need a shotgun, shells, shell holding device for reloads. A shotgun with choke tubes is preferred, since a Texas Star is included in the stage.
Chokes? It would be a good idea to warn the shooters with the short barrel cylinder bore (slug) guns that they might not be competitive. I have RO'd matches where this problem arose; there were a lot of unhappy campers.