Sorry I didn't see this before. Like our esteemed craftsman, woodcutter, mentioned, pick a disc you can throw in the vast majority of situations. Use a mini (provided, or bring your own) to mark all your lies before you pick up your disc.
For everything else, just check out the PDGA rules. Even though it's not a sanctioned tourney, the vast majority of the tournament rules still apply. But don't let that make you nervous. This event will be pretty chill and should be a good time. Before everyone heads off to their tees I'm going to offer to spend a few minutes with anyone playing their first tourney. Because it's only one round, it should be a good way to ease into the tournament scene.