For Negan: We have a feeling Negan will be a popular costume this year, and for good reason. Slick your hair back, glue on a mustache, and then put on a black leather jacket, a red scarf, dark pants, a leather glove on one hand, and carry around a baseball bat covered in barbed wire.
For Rick: If you're going for an early version of Rick, a dirty brown cop uniform will do. In more current seasons, he's been strutting around in jeans, a plain white t-shirt, and a sheepskin jacket. Splatter it all in blood, make sure your face is covered in scruff, and you're good to go.