It is disappointing, and in some situations, dangerous, to forget certain items...
...like the time I forgot my sunglasses on a sunny day of back-country skiing, and gave myself partial "snow blindness" or sunburned eyeballs, which felt like someone had stuffed my eye-sockets with sand. And the time I forgot my warm hat — maybe not dangerous, but definitely uncomfortable and cold. I have learned that it's good for me to have a system for remembering all my gear.
Enter, “dude-building” (DB). It's not just for dudes. All people need outfits. It's just what Dave called it.
He was my room-mate in college and into climbing mountains. Clothing systems in high alpine environments are technical and complicated - various kinds of gloves, hats, glasses, goggles, insulating layers and so forth. In order to make sure he had everything, he'd take all of what he thought he needed and he'd throw it in a pile on the couch in the living room. He would then "build his dude" on the living room floor.
Dude-building (DB) is simply laying out all clothing in the shape of a person lying on the floor.
Dave would say, "Dude needs some long underwear" and he'd lay them down. "Dude needs a warm hat", and he'd place the hat above the neck hole of his long underwear. "Dude needs to brush his teeth" and so on.
Lay all your layers out on the floor and see them in the shape of a person. Everything: socks, hats, gloves, underwear, rain gear. Then you'll see if you've forgotten something or if you could take something out depending on the weather and where you will be hiking.
That's it. This makes it pretty hard to forget anything.
Here's a demo-video to familiarize you with the process.
This particular DB is for Chilly Late Fall or Cold Early Spring.