Are you looking for something that will keep you dry? Or just for a little warmth until the sun comes out? If it's the latter then a military style jacket could work but so could a lightweight cotton crewneck sweater or sweatshirt (since you don't seem to want a hood) or a cardigan if you don't want to pull it on and off over your head. If it's to keep you dry then I'm not sure military is the way to go - most of those (except bombers) are cotton (e.g. the M-65 field jacket and similar) and hence will get soaked through easily and take a while to dry out. I'd go with something like the Patagonia Torrent Shell - lots of other manufacturers make similar waterproof-breathable rain jackets so you don't necessarily have to spring for Patagucci but it represents the basic concept. That type of jacket is really the only thing that will keep what's under it dry in a downpour. Except an umbrella, which has the virtue of not adding a layer.