Accessories
For those who want to identify with their character but don't want the complication or expense of an entire costume, a single accessory is a great way to give a tangible touch to the role playing experience. A medieval bracelet or signet ring is a way to connect to a fantasy character such as you might play in "D&D." For games such as "Vampire the Masquerade" where most characters are associated with a specific clan, an accessory bearing the clan sigil is a possible idea.
Decorative Costumes
For those who want to make a more complete costumed appearance at an RPG or LARP session, some simple ideas provide you with a complete costume. Capes, cloaks and robes are all easy ways to dress up for a medieval costume. These are easy to make and are also available in large supply from most costume or Halloween stores. Choose a color that associates well with the class or background of your character, such as a green cape for a woodland elf or a black cloak for an evil wizard. Some LARPs may have rules about what types of costumes are required or allowed for certain types of characters.
Functional Costumes
Functional costumes are used in some LARPs that involve actual combat. These costumes should involve armor such as chain mail or padded leather armor. The weapons used are called "beaters" and are made to resemble a real weapon while being made out of dense latex or foam in order to be safe for use in the mock combat. However, these swords can still smart when swung hard enough, so the armor, helmets and other protective gear is functional as well as decorative. Other systems don't permit the wearing of any metal armor to prevent accidental injury.
Custom Costumes
If you want to truly look your best at your next role playing game get together, nothing will beat a costume made by a professional costume designer. Provide a costume designer with a detailed description of your character and what you think the costume should look like. They will take measurements and craft a custom costume that fits you correctly. The decision to use professional quality costumes is sometimes made by a group that wants everyone to look as good as possible during gaming sessions.