"As I continue to train for my half marathon, I'm running outdoors more in cooler temps. My typical tanks and short-sleeved shirts don't cut it in New York Fall weather. Luckily, I have this Athleta Speedlight Half Zip ($79). It's long-sleeved so it keeps me warm enough, but I don't overheat in it since it's still pretty light. The fabric is moisture-wicking for when I get sweaty (which is every time I run). It's the perfect layering piece: on top of a T-shirt if I need to take it off or underneath a warmer jacket for when it gets really cold." — CS