The dotted line with stars could be a side seam for men, and also for very early women's dress. Everyone who attends an event is expected to wear at least an attempt at medieval clothing. Garb need not be fancy. Call someone in advance to see if loaner garb will be available, or at an event look for the symbol of a key on a green or blue background. You may also wish to bring a small cloth in case the table is uncovered, a fork, a bowl, small containers of sugar and salt, and a plastic trash bag to put dirty feast gear in after you have eaten.
Many people bring their own beverage, but often some form of drink is provided.
Iced tea, lemonade, and water are common. For outdoor events, it is wise to bring a folding chair or a blanket to sit on. Carry a portable supply of water or other beverage, especially if you will be in the sun for part of the day. Bring a hat or other sun-shade for protection. Working on a craft, project, or game can be a good way to meet others at an event when you tire of observing.