Cycling cape
I used one of these for years to and from school in Cambridgeshire when I was a teenager (5 miles each way). Big enough to keep rain off the legs and feet and made of a sort of rubberised cotton, heavier than nylon.
Kept me dry in a lot of rain, and never remember having problems with it blowing about, although it did slow things down a bit. I seem to remember everyone having one. (Mind you, the roads were quiet, buses were regular, there were bobbies on the beat, zzzzzzzzzzzzz zzzzzzzzzzz ).