The British Army first constructed this piece of outerwear for their tropical-stationed soldiers who required light-weight items that would still hold up to the weather. As it evolved through society into more of a workwear staple, heavier construction became the norm and a new name—the work shirt—was born. Today, they're simply called shirt jackets or "shackets," as the kids say. And dollar for dollar, the most important item you could purchase for these unpredictable in-betweener months is a jacket that wears as well on 40-degree nights over a sweater as it does on 60-degree days over a T-shirt. Today's best styles are tailored to do just that, keeping you warm without a lot of bulk. Look for dark or earthier tones that easily go with anything you decide to pair with it, because you'll likely be getting a lot of wear out of it this fall.