There's lots of posts on where little bits of "Indy Inspiration" originated: Secret of the Incas, Zorro, etc...
Most recently, on the "Schott" thread, there was some discussion about the origins of 'the jacket' and Mutt's jacket as well.
THEN, there was _'s interesting, if somewhat flawed, thread on the popular use of zippers. I say 'somewhat flawed' because of a movie I re-watched not long ago with an eye more critical towards costuming. The movie: Only Angels Have Wings. The movie was released in 1939, stars Cary Grant, and is an excellent place to get an eyeful of A-1 flight jackets and inspiration for scores of other adventure stories and movies. The primary antagonist of the movie is the pressure under which the pilots in the movie work, but adding to the tension is the introduction of a character called Bat MacPherson. I won't go into the whole story here, however, watching the scenes in which MacPherson flies, he wears a jacket that is VERY Indy-esque; no snap down collar, no elastic on the cuffs, sliders just above the waist, and a zipper. I can't recall at the moment whether or not there was a storm flap.
I've scoured the internet in search of a still to no avail, unfortunately, and naturally I couldn't expect anyone to rush out to buy the movie just for screen caps. But you should see the movie: it is excellent and the inspiration for Tales of the Gold Monkey and the old Bugs Bunny gag, "Calling Barranca...Calling Barranca..." ( and an Indy character name! )
_: if you see this, I can't remember your timeline on popular use of zippers, but I would assume you could peg the costuming in this flick to 1938, or so. So we're in the ballpark for an Indy jacket with a zipper. Not meant to be argumentative; just a point of interest. Being a 'jacket guy', if you haven't seen the movie, you should. If that's not enough, there's Rita Hayworth
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