Some of my costumes from when I was younger include a smiley face pumpkin and a pirate. One year my brother was a ninja turtle.
To make the pumpkin to you take orange material, sew it at the top with elastic while sinching the material, and do the same at the bottom. Sew on the eyes, nose, and mouth. You can add green pompoms for additional decor.
The pirate I wore black pants, a white and black striped shirt, and a patch over my eye. I also think I had an aluminum foil sword.
The ninja turtle was really neat. Green sweat suit- material bandanas around the head with eye holes cut out, arms and legs. Purple-Donatello, Orange-Michealangelo, Red- Raphael, and Blue-Leonardo. For my brother I think he had nunchucks (Donatello) made out of painted toilet paper rolls. The turtles need a shell too. You can make one like a pillow, or attach something to a backpack that comes off easily for rides.
Of course there's the traditional princess. You can get neat tiara's off of ebay for 10 dollars.