Here's a list of shops and vendors you can purchase your costume from (if you don't already have one). Dress according to your comfort level. You don't have to go all-out if you don't want to.
Popular Renaissance Festival costume themes:
-Historical Eras (Medieval, Tudor, Elizabethan, Italian Renaissance, Roman Empire)
-Fantasy (Elf, Fairy, Sprite, Wizard, Witch, Steampunk)
-Rogues (Viking, Celt, Pirate, Highlander)
-Cosplay (Lord of the Rings, Game of Thrones, The Witcher, Dungeons and Dragons)
-Create Your Own (Mix and match from different themes)
**Inspiration pics at bottom of page**