For me the most important piece of equipment I own is my clothes. Clothes are the number one used item for everyone and probably the first thing you notice if it doesn’t work! I personally organize my layers into these categories: Base Layer, Mid Layer, Insulation Layer, Outer Shell, Accessories. This partially denotes their uses but for the most part it’s got to do with how I organize it in my head when I’m packing and buying gear so I only take what I need and only buy pieces that fill gaps in my system. Most people and places don’t denote the difference from Base layer and Mid layer, base being long and short underwear and mid being t shirts and pants. Since I use my long base layer as pj’s as well as insulation and rarely wear my long underwear by itself, I always take both and making the distinction helps.