Some easy homemade costumes are a jellyfish and a silent film star. Some especially creative ideas to make at home include a piñata, a bag of jelly beans and a bath puff.
To make a jellyfish costume, start with a clear umbrella. Attach lengths of ribbon, fabric or string all around the umbrella to look like stingers. For the silent film star, wear all black clothing (preferably something that fits with a 1920s and 30s-era look). Use white face paint and all-black accents, such as lipstick and facial hair. For a prop, make a small sign with movie dialogue written on it.
A piñata costume can be made by attaching colorful strips of crepe paper to any outfit. Use a lot of individual pieces for the best results. For the bag of jelly beans, cut arm and leg holes in a large clear trash bag. Draw a large "Nutrition Facts" label on one side. Fill the bag with colored balloons and wear it over neutral clothing. Tie the neck closed with a brightly colored ribbon for an added touch. To make a bath puff costume, attach large bunches of colored tulle to a dress or to a pair of shorts and a t-shirt using pins. The tulle pieces can also be sewn on.