Intro: No-Sew M&Ms Costume
All you really need for this costume is some fusible web, white fabric, and a sold colored shirt (sweatshirts are nice to stay warm in th fall). Attach the fusible web to the white fabric, trace or free hand draw an "M" in it, cut it out, and iron it onto your shirt.
This is cheap and easy. I made shirts for my husband, son, sister, niece, and myself. We couldn't find a solid shirt in my niece's size, so I got a hoodie, and cut the M in half and did one on each side of the zipper. All together we were a "pack of M&Ms."
I did Ms on the front and Ws on the back, cause that's what they look like, and had to listen to people call us "M&Ws" all night. So you may want to do Ms on front and back, but then people will tell you how wrong it is, so if I did it again, I would only do it on the front.
You can put a little more effort into it. My son was the red M, and I sprayed his hair with temporary dye, and made him wear his read Converses. I was the blue M and put the effort in to wear "blue" jeans. I also had blue eyeshadow, and blue lipstick, that's why I look a bit frost bitten in some of the picture.