For me, the starting point that makes a lot of it way easier is to focus on layering. Anyone who lives in the Bay Area will instantly understand it: you don't build outfits for different weather, you build outfits for all weather that just depend on how many layers you've got on. For example, no cold-weather coats: instead you pack a feather-light and very foldable rain shell, layer it over thin sweaters for cold weather (multiple, if it's cold enough), and wear it directly over a light outfit for warm rainy weather.