Need a Halloween costume idea?

I'm 14 years old and I'm a guy, and I like Call of Duty, Minecraft, the Avengers, etc. I need some costume ideas for Halloween. I have not bought a costume and I would like to avoid that if possible, and I do not have a ton of time to build an awesome costume out of cardboard or something like that. I have some stuff at home that I could use, including some gray, black, and blue shirts, a few pairs of khaki pants, a pair of jeans, a black jacket, black shoes, etc. Any ideas for a quick costume that is fairly cheap or does not cost anything at all?