Wizards are known for long, loose belts. Opt for a knit belt or one made of fabric over a leather or plastic variety. The belt goes around your waist and not your hips, pulling the robe slightly towards your body.  Most department stores and clothing stores sell long, loose belts meant to wrap around your waist. Look for a color that compliments your wizard robes. You can also buy a belt online. If you really want to solidify the wizard look, you can buy a wizard belt from an online costume store. Wizards are known for wearing long, pointed hats. Most conventional hat stores and department stores do not sell wizard hats. Luckily, you can easily find a hat at a local department store.  If there isn't a costume shop near you, you can order a hat from a store online. Opt for a somewhat floppy, pointed hat with a wide brim. If your hat is not decorated the way you like, glue or stitch on stars. Pick a hat in similar color to your wizard robes and cape. If you're going to a costume party dressed as a wizard, a mask may help. Many people think of wizards as old and wise. You can buy an old man or woman mask at most costume stores or online. This can really help solidify the wizard look. However, not all wizards are old. If you want to dress as a younger wizard, you should probably forget the mask. Wizards are known to carry wands. Most costume stores sell fake wands you can buy for a reasonable price. You can also find a wand at toy stores, especially if they sell products from franchises like Harry Potter. You can also make your own wand if you can't find a satisfactory one near you.  Pipe cleaners can be used to make a wand. Simply You can twist together pipe cleaners until you have a sturdy, thick wand. Then, attach a shape made of construction paper to the end of the wand. Something like a star or an orb would work.  It can help to decorate the star or orb in glitter. This will give it a glowing appearance. Many wizards carry staffs in addition to or instead of wands. If you want to solidify the wizard look, consider carrying a large stick or poll with you.  You can buy fake staffs at costume stores or online. You can also get a large, thick stick from outside. Make sure the stick is free of bugs and dirt before bringing it into your home. You can buy a spell book online or at a local costume store. If you're going to a party dressed as a wizard, carrying a spell book around can help. It will give you the mystical look of a wizard.

Summary:
Wear a long belt. Invest in a wizard's hat. Consider a mask for a costume. Buy or make a wand. Consider a staff. Carry a book.