I've discovered one of the easiest and quickest things to do is be a literary character. I managed to pull my costume together tonight after deciding on a character from one of my favorite books! In my experience, lots of literary characters have a rather simple costume, and most that I can think of can be made from random odds-and-ends around your house.
Zombie is the easiest thing i could do i got alot make up blood ect day after halloween last year real cheap
Rip up some old cloths put blood on them put on pale make up cuts scars ect lots of blood and thats all there is to it. plus its the most fun to act like.