For the past several years, I've been Jason Voorhees. I use a costume I bought online for the pants and jacket, a hockey mask over a rubber rotting Jason face mask that I also bought, an old pair of filthy work gloves to cover my hands, thick boots soaked in mud (helps keep me cool, as well), and a plastic machete wrapped in silver tape and soaked with some dripping red food coloring.
I'm thinking of adding a chain around my neck this year to complete the Friday the 13th Part VII: The New Blood look. That's what the costume itself is based off of, not the newer Freddy VS. Jason design where Jason magically has darker, cleaner clothes.