The term "mid-century modern" drives me nuts. I'm old enough to remember when we called the style "modern." It's the "younger" crowd who coined the phrase not that long ago. It's like they discovered something us old timers have recognized for years. I prefer "retro" as a description of the style.
That being said, the style of the time was a change to simplicity and minimalism. A lot of quilt patterns we call modern would fit the bill. A lot of Amish quilts could also be considered MCM with a change of color. One of the big change at that time was a changed to color and texture. For example- if one took a simple 9 patch, or HST, or 60 degree triangle quilt in a simple layout, but changed the colors to something acceptable in the design of the times, it would look as MCM as you can get. As much as design, colors and textures did as much for "nailing" the style as anything else.