The next thing and one that was hard for me to turn loose of, was a ton of extra clothing. No one wants to go into the woods and be wet, cold and miserable. At home most people have drawers and closets of extra clothing and can change shirts, socks and underwear on a whim. When your home is on your back you just don't have that luxury, as a result, it is very important to carry the right items. You should maybe put more thought into your clothing than any other section of your backpacking gear. First and foremost synthetics or wool is king and cotton is miserable! Whether it is the middle of the summer or freezing cold, what you are looking for is something that is moisture wicking and quick drying. Clothing that does not absorb water and cause excessive chaffing is vital. There are tons of options even from your local Walmart, one of my favorite lightweight shirts is a Dickies brand breathable, lightweight shirt that costs about $11. How much spare clothing do you need on an average backpacking trip? Really a spare pair of socks is about it most of the time. My normal spare clothing besides what I am wearing, 1 pair of socks, 1 pair of underwear, 1 t-shirt and one lightweight pair of running shorts and a lightweight windbreaker. Now of course according to weather it changes and I will add a complete set of fleece long johns for cold weather but basically that is it.
One early spring trip a few years ago an unexpected cold front dropped the night time temps down into the 30s. On the morning after that front came through, I got up to stand next to the fire and told the guys that if the temperature dropped another 2 degrees I was leaving. I literally had on every piece of clothing I had. Which brings me to another point, sometimes you just have to embrace the suck, but with careful selection of the few things you do carry you may be surprised at just how comfortable you can be.