One item that any Americans reading this might not be familiar with is the Buffalo shirt. While it’s not an issue piece of the British military uniform, it should be because virtually everyone in the Armed Forces has one. Available in various styles now, the standard Special Six shirt is an over-the-head top, lined with fleece and with a shower-proof outer. There are also ventilation zips down each side. This thing is incredibly warm and you could wear it and a T-shirt during a standard British winter and not get cold. If it gets wet, it dries in no time and it weighs very little. It’s light-weight and while the pack size isn’t that small, a few compression straps soon take care of that. It’s a fantastic bit of kit and it’s one that I’m sure almost every British soldier and Marine has.
I’m not sure if there is a similar item used by those in the American military, but the Buffalo has spawned a range of copy-cat products, the best and most popular of which are made by Snugpak. If you’re in the service or just an outdoors sort of person it’s certainly an item to have a look at.