This thing called "Layering" is generally accepted as the best way of dressing for outdoor activities. (But you know what they say about conventional wisdom.)
There is the Base Layer, the Insulation Layer, and the outer Shell which all work together, all three of them, to provide maximum protection against cold temperatures, moisture, and weather in general.
Layering in clothing is one thing, but if you stay home layering around you don't get tired at all. In fact, you can actually catch up on your sleep while layering around. And you don't have to wear any clothes at all, or even maintain consciousness.
Well, back to the outdoors and that layering thing...
This is the approved and officially-sanctioned method of wearing all your clothes at once. Get this down and no one will point at you and snigger. Better yet, they won't throw rocks either. Get it perfect (while wearing new, fashion-compliant clothing that still reeks of petrochemicals) and you may even be asked to teach a class on wilderness survival.
Since Layering, if done according to established practice, is a buzzword-dependent technique, we can't call these layers "one, two, and three", or even "inner, middle, and outer". Nope.
Instead let us use these terms: Thermal Underwear, Insulation Layer, and Outer Shell Layer. Hot damn — now we're talking. Can't tell how you feel, but I'm starting to get tingly already.
So.
Next to your skin you wear a thin layer of reasonably warm, reasonably fuzzy stuff — your long undos, or Thermal Underwear. This keeps your skin warm and helps to wick moisture away from it. Fair enough.
Next up, the Insulation or middle layer. This mainly preserves what heat you have by holding in place an even layer of still air near your body. Still air is a pretty good insulator. Keep that in mind and you'll do fine, if you also add the third and final layer, The Shell.
The Shell keeps your fuzzy stuff from direct contact with the outer world and form a barrier that traps that bubble of still, warm air inside where it belongs, next to you. The Shell also deflects wind, rain, snow, and flies. And mosquitoes. And those other, even bigger flies that have pointier teeth and electric drills and tiny but sharp chain saws. Them. Deflects them too.
This shell layer should also be reasonably breathable if possible. What this means is that water vapor should be able to diffuse through it from the inside to the outside so that you don't end up all clammy, or even worse, stuck to your underwear by another layer, a layer of ice.
On a cold, cold night, you should go to bed by adding the very final layer, your sleeping bag. It's a layer. Think about it.
So stay warm. We're counting on you.
Special bonus postscript section, if you care.
Layering is also how to make a decent sandwich.
For traditionalists, just put a bunch of sliced cold meat between two pieces of bread and eat while playing poker.
For the average person, buy one.
For hikers, put layers of anything edible between layers of anything else that's edible (definitions may vary, but bread is nice on the outside, if you have any of it), add spicy goop in the middle if you have some of that too, and eat while scanning the landscape for anything that might be gaining on you.
If you get even a bit of the goop on your clothes you'll have to peel off a layer and bury it or else something is all too likely to come out of the dark of night and eat you back. Or at least give you a good, thorough snuffling, and do you really want that? Think it over carefully before proceeding.
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Have anything worth adding? Then try sosayseff+eff@gmail.com
Me? Still trying to lick the goop off my $600 waterproof-breathable fantasy jacket.