In "The Longest Day", John Wayne has a pouch attached to his helmet. What was it for?

http://www.med-dept.com/articles/the-parachute-first-aid-packet/

It is a first aid kit.

It was a parachutist's first-aid kit. According to this site, it was a mistake:
http://www.paratrooper.be/reviews/movies/
Speaking of classics, this is perhaps the biggest one. The DVD pictured here is the original black and white version, but a color version also exist and if you don't know any better, it looks like it has actually been filmed in color. The story is based on true events (duuuh!), but it's riddled with uniform, insignia and equipment mistakes. John Wayne with the parachutist first aid kit on his helmet, for example. Really sad if you figure that in those days there was no need to reproduce anything, and there was no lack of veterans to advise the director.