Clothing: a very personal issue. I won't in any way suggest what is best, or what you should wear - it is an individual decision. In the past, I simply recounted what I wore and what I thought of it as a rider. I decided to try this topic another way; from the inside out.
As a young rider in the 60's I wore a jacket sometimes, jeans, combat boots and gloves, and a 3/4 helmet. Pretty much the uniform of the times. Thankfully, I never got to really evaluate the protection any of it afforded on the minor crashes I had. I did better on dirt bikes, but in those days there was no armor or any kind, just a jersey and padded leather pants. Fine enough. In the past 15 years I've learned quite a bit worth passing along - I think.
Innermost Layer:
Butt and torso: Much is made of wicking garments like the venerable LD Comfort Shorts linked below. I wear these as well as the tights, and they do an excellent job of moving moisture away from my skin to the outer garments to be, eventually, evaporated. The benefit is dry skin minimizes the effect of sitting in wet cotton undergarments for hour after hour on hot days and forestalls Monkey Butt. Add a little non talc powder and one is about the driest one has been since clean diapers. These wicking shorts work best when there is an absorbent layer next to them like a cotton short or pant. The downside is with whatever one's outer garment is. Sliding down the road on your butt generates a lot of friction which means heat which means synthetic undergarments melt onto your skin if the slide is long enough.
Cotton is a better insulator in such cases and does not melt like a synthetic fabric. Melted fabric in my skin is an unappealing thought - it is akin to melted plastic and can't be all that much fun in the ER as they scrub that off you to healthy unburned tissue underneath. So, the options seem limited to Monkey Butt inducing underwear or dry skin and maybe melted underwear in your hide. Neither is appealing.
Research leads me towards Merino wool undergarments. As of this writing, I don't own any and have not tried any on a bike. As a backpacker, I can tell you the stuff works, keeping a guy warm and fairly dry in moist environments, seems to dry fairly quickly in the lighter weights, and does not stink all that bad after a day or two. I always wear long sleeve T-shirts so my arms have some abrasion/heat resistance.
Feet: I wear wool socks. Breathable boots seem to be a good thing in theory but in practice become non-breathable as they get dirty and the pores clog. Wool keeps my feet warm and dry in cold climates and in hot climates dry out quickly strapped to the bike so they flap in the breeze. I change them a couple times a day, and hit a laundromat more often in hot conditions to wash my undergarments, socks, and so on.
Hands: I wear the lightest gloves I can for the conditions I'm in. I need tactile feel for the throttle, clutch and brake levers. I find heavy gloves diminish the feel and I don't like that. Heated grips make up for the thickness and many light weight gloves have wind stop membranes and I'll choose these if the trip takes me to colder climes. I do not care if my hands get wet. Gloves tend to dry out reasonably well overnight if placed next to a room heater or wrapped in a motel towel. When I rode boxer engined bikes I'd just lay the gloves on the cylinders when I went into a store for coffee, and they would be dry when I returned.
Head: I thought a neck gaiter, or a light balaclava would be a good thing and if it is cold and my jacket does not seal well at the neck they can indeed be valuable, and they take up little space in a tank bag. The major downside is when it rains. I discovered a balaclava will direct rain water from your neck down your back inside your jacket. Leaving the thing outside your jacket provides little improvement.
Mid Layer:
When it is cold, I will wear either tights under my pants, or light weight sweat pants. I will wear a long sleeve T-shirt and a Gerbing electric jacket as a mid layer. I used to wear electric vests as the theory is keeping your core warm keeps your arms warm. That is BS especially when you ride long days in the cold.
Outer Layer:
Clothing: It depends on the motorcycle for me. If I'm on my sport bikes I will wear leather pants because I like the way they feel on the bike. I may wear a corresponding leather jacket, or the Comfort Shell Jacket. On the GT I wear either my Aerostich Roadcrafter or the Comfort Shell ensemble. I like the convenience of the Roadcrafter and I forces me to wear all my protective gear as it is a one piece suit. The other stuff is lighter to wear. Primarily, I'll use the Roadcrafter if on an Iron Butt Ride. In either case I wear my stuff and keep it zipped up and closed up as much as I can tolerate. Doing so in the heat creates a micro climate inside the garment that is cooler than riding around in jeans and a T-shirt. Your body stays moist, dehydration is minimized, and at night you stay warmer longer. If it is hot I wear a breathable shell like the BMW Comfort Shell. The pores on this garment open up in heat to let moisture through and close when it is cold so it becomes a wind barrier. The jacket has great vent zippers, and it works very well for me. The same applies to pants and I like the kind that zip to my jacket so they don't get separated during a slide and keeps my armor where it needs to be.
Boots: I wear the toughest I can find that work with the bikes I ride. I like lots of ankle support, shin protection, and a good non slip sole. I like thin hard soles so I can feel the pegs as I ride.
Helmets: I wear the best I can afford. Arai full face, or Shoei Multitech if I have to wear a flip front.
BMW Tourgard jacket. These jackets were very expensive retailing for over $650 and I often wondered how that was justified. When BMW put them on close-out at half price I jumped at one. It now is used as my winter riding jacket. Great CE armor, back protector and made of a Kevlar/Nylon/Gore-Tex material. Has a removable quilted liner. Wrist closures are superb as an inner and outer seal my riding glove so water can not get in. Though I have my heated jacket with me I have rarely used it in our typical rainy 40 - 45 degree days. I used this jacket this past September riding through 100 degree temps as well as 45 degree rain. Very good stuff indeed. Has been replaced with the Street Guard line of garments.
BMW Comfort Shell Jacket. I just acquired this garment and love it. The material, a sort of Gore-Tex membrane, opens when it is hot to let moisture out and closes when cooler to conserve heat and become wind proof. There are stretchy panels so the jacket does not bind. It zips nicely to my BMW City Pants and to my BMW Atlantis 4 leathers. I wore it in 95 degree heat and 45 degree hailstorms this Sept 2008 and it did as advertised. I will add that the back pad is huge providing protection to the kidneys, and the armor in back, elbows and shoulders is the moldable kind conforming to your body as body heat warms it up.
BMW Atlantis 4 Pants. These leather pants are waterproof without resorting to a liner shell to achieve waterproofness. They reflect sunlight and are much cooler in hot temperatures than other leathers. They zip nicely to BMW jackets and are very comfortable. The armor molds to your body as it is warmed by body heat maximizing comfort in the knees and hips. Very good stuff.
Aerostich Roadcrafter. I stopped in Duluth, MN at the Riders Warehouse and bought this garment. As far as I'm concerned it is the best riding gear for long distance riding. Click on the link and get the details. No garment is perfect all the time but this is damned near the case. I wear it daily for commuting with my work clothes on underneath. On long rides I wear light clothing underneath, and when it gets cold I add my Gerbing jacket. I have been dry in a Houston downpour and relatively cool in 100 degree heat. I can add ice to the back pocket when it is hot and open some vents. The protection is awesome. Put one of these on your list of things to get.
Gerbing jacket I used an electric vest for a few years and was content with it untill I was riding home from my 50CC. Going over I-5 by Shasta was cold. My body started out warm but my arms were cold and that eventually made the rest of me cold as well. I acquired a Gerbing jacket with heated sleeves and have never been cold again. Don't buy a vest when you can get a jacket.
LD Comfort Shorts If you ride long distances you will get hot spots on your ass. Typical cotton undergarments absorb moisture to saturation then you sit in damp stuff getting more and more uncomfortable. LD Comfort garments are like runner's or cyclist shorts in that they stretch 4 ways via the Lycra layer but the Lycra as an outer layer is bonded to an inner layer made of a hydrophobic material that wicks body moisture to the outer Lycra. It is then evaporated. The result is you stay dry and hot spots are now the result of a bad saddle design.
The boys in Hoquiam, WA make these things - check the link - they are the best long distance garment made. Period. End of testimony. Buy a couple of pairs and enjoy your Saddlesore 1000 instead of enduring it. I have a couple pair of the shorts but recently tried the tights - I like those better.
Helmets I have experience with:
Arai Quantum II - best I have used as it vents well, is fairly quiet and quite light in weight.
HJC Symax - Inexpensive and when it rains it sucks. I know this is a popular helmet but I do not like it one bit.
Schuberth - the flip front is the best helmet I have of its type. It demists well, is strong, has a flip down sun visor and is fairly quiet for a flip front. No longer available in the U.S.
Nolan N100E - about as useful as the HJC Symax.
Shoei Multitech - Very quiet on my K1200R but one of the noisiest when riding my GT. Has to do with the slight turbulence produced by the GT's windshield.