Cory Bernat has curated an extensive online image gallery of war-era government posters related to food, food production, farming, backyard gardening, and rationing. The images come from the US National Agricultural Library.
One thing I noticed: the large number of posters promoting vegetarian protein sources, in order to conserve meat. Another: you know how gluten-free diets are more common nowadays? You'll find many posters in this collection referencing "wheatless" diets, and promoting other carbs like potatoes and corn. And finally, some of these would fit in quite well with my colleague Mark's Made By Hand book. Below, the poster from which the title of this gallery came: "Beans are Bullets."