This lightweight vest is the perfect layer for London winters, where temperatures and precipitation can vary widely on any given day. Pack it away in a tiny pouch and bring it along for any occasion, from outdoor runs to a day on the town. Best of all, the vest is only $50. LINK.
*Model in photo (from uniqlo.com) is not me. Shocker.
Runner Up: Nike Dri-FIT Wool Half Zip