Bear scout adventure Grin and Bear IT: This site has a bunch of fantastic DIY carnival games and activities. including this simple KNOCK DOWN game. All you need are disposable cups and a cute sign!
Have the cups spell out PTA Ping pong toss carnival game can make "witches hat" with black cups
East Coast Mommy: Carnival Games and Activities paper towel tube and pipe cleaners!
25 Tutorials for a DIY Carnival - Ticket streamers, great for prize table decoration!