Supplies:
Solid print T-shirt
Permanent markers (or better yet, fabric markers)
Find a hero you like. See how they make their costume. Convert to a T-shirt. Very simple, very satisfying.
I did Wolverine from Marvel's X-Men. If you have to draw a lot, make sure you have a few markers available as you can run through them quickly. Also, permanent marker, despite its name, does run if you wash the shirt. Wash by hand to avoid too much running (and to keep other clothes from getting markered), or better yet do not wash the shirt until after Halloween.
If you are looking for more elaborate costume ideas, see all the posts here
