You might dress up stylishly. You could make a splash and dress up daringly. Or you may dare to dress up barely. You could dress up horribly. You may like to dress up cutely. Or, perhaps dress up acutely.
You could wear them to your "clown" job at the circus. You could even wear them to your wedding. You could even wear them at Halloween, when dressing up is involved. You could even wear them at kid's birthday parties.
you could dress up in the flag or you could dress up as a dragon - its on the flag Or, you could dress (if you're female) in the Welsh lady dress
If you want to dress up like a person from Egypt you could dress up as a Pharaoh or a queen. You could also dress up as one of the gods.
You could dress up as a killer or a kid.
You could dress as an airline hostess or an angel. You could dress as Alice in Wonderland or an Arabian princess.
You could dress as a senorita or a school girl. You could dress as a surgeon or as the sheriff.
You could dress as Tarzan or as a tramp. You also could dress as the Tin Man or as a train engineer.
You could dress up as a person from West Side Story. Or you could google "musicals" on the images and see what the characters look like.
You could dress as Satan, Spiderman or Superman. You could dress as a safari hunter or as Sherlock Holmes.
You could dress as a waitress, witch or a wizard. You also could dress as Whoppi Goldberg or Wonder Woman.
If you mean a costume idea, you could dress up as a can - either a tin can or a trash can.