Montbell XL windshirt has been thoroughly tested in a light drizzle and modest output and keeps you dry and pretty warm with just a long-sleeved synthetic crew neck top at around 40F or 5C. Probably the most breathable of all my rainware, fits in a tiny little pixie stuffsack that gets lost in my pockets.

Cost $50 including shipping, weighs 3.7 oz, and I'm happy with the hood and the construction. Would not stand up to rough use (rocks, knives or fish-hooks), but will repel nasty looks and pointed remarks about weight weenies.