Any discussion of gear has to start with the Ten Essentials. These are things you should bring on any outdoor adventure. The Wikipedia page covers it well.
Nothing is more fundamental than boots. My approach to footwear has evolved into two general kinds based on the hike I am planning:
- warm weather all purpose boots for most situations
- waterproof for snow and streams
For general all purpose warm weather, I have had good luck with the Merrell Moab Ventilator. It is rugged enough and grippy enough for most situations while remaining comfortable on longer days. I am on my third pair after wearing out the first two over 400 miles each.
I used to have Vasque Pendulum II GTX trail runners, but they were too small in my size and caused issues going downhill.
For snow and streams, I am using Vasque Snow Junkie Waterproof. The few times I've taken them out, they have stayed dry, but are rubbing blisters on my heels. I don't do a lot of snow, but will probably get something else when the time comes.
I prefer all wool socks for comfort, warmth, and wicking. Smartwool and Darn Tough have both been very good.
I tend to play rough on mountains, or rather the mountains tend to play rough with me. It is not uncommon for me to shred pants in brush, climbing rocks, or sliding down rocks or ravines. So, I prefer inexpensive pants. For warm weather, I have multiple pair of White Sierra convertible hiking pants and replace a pair as they get destroyed. I have one pair of Columbia shorts. For snow pants, I have one pair of Columbia Bugaboo.
I have both long sleeved and short sleeved versions of Nike Pro Combat wicking tops. I often wear a short sleeved on top of a long sleeved on cool days. They have worked well in many conditions. I have one pair of REI brand base layer bottoms, but have rarely used them so don't really have an opinion.
If you are wondering why you might need compression underwear, you probably haven't done a 15+ mile trek in 90+ degree heat. Long hikes mean friction and friction in the wrong places will leave a lasting impression. Compression underwear reduce friction where it counts the most. To be sure, I also recommend BodyGlide anti-friction balm.
Right now, I wear Nike Pro Combat and they are working great for me, but I can't compare them against other brands since I haven't tried other brands yet.
I just replaced a two year old REI brand fleece, which was reasonably warm and durable, with a Mountain Hardwear Monkeyman 200. I've worn the Monkeyman several times in cool and cold weather. Wow, does it ever retain heat. It is a solid middle or outer layer, tough, and durable.
I have a light shell when I just need wind protection and a heavy shell for snow. I recently replaced these pieces and splurged a bit. You can definitely find similar, less expensive jackets. In fact, my first heavy shell I bought used on Craigslist.
My light shell is a Marmot PreClip jacket. It is very light, waterproof, windproof, and breathable. It is not designed for warmth, but ideal as a top layer for cool, windy, weather. I wore this on Mt. Saint Helens.
My heavy shell is a Columbia Bugaboo. The Bugaboo is waterproof and has a zip out fleece with an OmniWarm liner. I have worn it with great success in the middle of a winter storm. In this class of winter jacket, it is very affordable.
Kahtoola Microspikes for moderate, slippery hiking and Grivel G-10 New-Classic Crampons for more serious snow and ice. Although I enjoy it, I don't do a lot of snow and ice hikes. I've only used the crampons once and they performed perfectly. For crampons, I think the most important thing is make sure you get steel and not aluminum so you can handle rocks and mixed terrain.
I use inexpensive Kelty adjustable twist-lock poles. They have been durable on my toughest hikes. I tried higher end LEKI Khumbu poles, but the locks kept collapsing on me. I am only 160 pounds so I should not be able to collapse the locks. Maybe I just had a defective pair.
I have evolved into three packs based on duration or weather conditions. A light pack (18L capacity) for stuff under 9 miles. A workhorse pack (24L capacity) for most hikes, and a larger pack (36L capacity) for very long or sub-freezing hikes. The CamelBak hydration system has worked well for me, but I haven't tried any others.
My light pack is an Osprey. My workhorse is a CamelBak with a 3L hydration bladder. My larger pack is a Marmot top loader with no hydration system. I found out on some sub-freezing hikes that water froze in my hydration tube and the mouthpiece would ice up, so I only take bottles of water and gatorade when the temps are going to stay below freezing.
A GPS is optional, but a very useful supplement to topo maps and compass. I have only used Garman eTrex receivers. They are compact, tough, and pretty easy to operate. The eTrex models use a trackpoint for menu navigation and operation, which I like. Higher end models use a touch screen that can't be used when you are wearing gloves, unless they are special electronic friendly gloves, and even then may not work well. I have lost a couple so I use a carabiner and clip it through my pants loop now. It runs on two AA batteries and I always carry spares. There have been many lively debates on the pros and cons of a GPS. I clearly think they are worthwhile. I try to upload all my recorded tracks to peakbagger.com to make them available for other hikers to use. I always appreciate it when other hikers share their tracks.