Sailor costumes are fairly simple to make because they are easy to recognise. You can use white clothing with navy-blue accessories or navy with white detailing. If you're handy with a needle and thread or sewing machine, you can sew the complete costume. Or you can patch together a quick and easy costume from a variety of materials.
Turn the white trousers into sailor's bell-bottoms by making a slit about 12 inches long on the outside bottom of both legs. Buy enough fabric in a close shade of white to fill in the triangular spaces. Leave a half inch of extra fabric so you can turn it under and sew it to the pant legs.
Make a white shirt with loosely fitting long sleeves. To get this look, buy a white shirt in a larger size and cut off the cuffs. Hem the sleeves or turn them under and secure them with tape.
Roll a navy blue bandanna long and thin, or use a narrow piece of dark blue fabric. Place the bandanna under the collar to make a scarf. Knot it in front.
Cut the poster board in a slightly angled circle that will fit your head to form the sailor's cap. Tape the ends together, angling the brim so it flares out at the top. To make the crown, tape the coffee filter inside the brim. If you're handy, sew the crown and brim together using white fabric with a cardboard lining to make the brim stand up.
Cut a small rectangle of navy-blue construction paper to create a label with your ship's name. Use white ink to write the name of your ship on the tag. Begin it with "U.S.S."
Wear black shoes to complete the outfit.
For a different sailor look, wear a red-and-white striped T-shirt under the white sailor top. Add the Navy insignia to the sleeve by creating it from construction paper. Look for white bell-bottomed trousers in thrift stores.