First of all the theories of UL clothing systems as I understand them:
Performance: finding designs and fabrics that deliver the optimum protection and breathability for the weight.
Layering: assembling a selection of gear that works together to keep warmth in, transport perspiration out, and provide protection from the conditions at hand: intense sunlight, bugs, cold, or precipitation. Each garment should be usable alone or in concert with others with as little duplication of purpose as possible
Multi-use: Rain gear as shelter, base layers and insuation to augment sleeping gear, etc.
Caveats: durability, insulation layers that duplicate wind protection (my personal grail), breathability, single-purpose items (like soft shells, that commit considerable weight but only deliver in a narrow band of conditions). Much of the theory is based on multi-day hiking and a wide range of conditions vs. day hikes with a narrower range of temps and precip.
Needs: retaining core body temperature (and comfort), transporting perspiration from clothing layers, protection from bugs, intense sunlight, and precipitation.
Base layers: typically light layers of polyester or merino wool. Performance aimed at moisture transport and quick drying while preventing convection from skin. Available in various thickness and weights to act as insulation as well as moisture transport.
Insulation: typically goose down or polyester fill with thin fabric coverings. Also polyester fleece that requires no extra covering. May be a vest or sleeved.
Outer layer: abrasion, sunlight, bug, wind/convection, and light precip protection.
Rain gear: protection of other layers from precipitation. May also be used for wind protection or shelter.
Practice: forget everything you know about dressing for home/work/street!
My personal specifics:
Base layer: Patagonia Capilene, GoLite C-Thru or similar "silkweight" short sleeve and/or long sleeve tops, briefs, and long johns. I typically have two tops: one short sleeve, one long. Long bottoms for colder, wetter weather.
Insulation: Patagonia Micro Puff vest, Burton Heater polyester fill pull-over (like Micro Puff), fleece sweater, or down sweater for extreme cold. Varied to suit season/conditions/weight
Bottoms: nylon or polyester shorts, long pants or zip-offs. Ex Officio Amphipants, REI Sahara pants/shorts/zip-offs, REI Cordura pants, running shorts with breifs and GoLite Whim wind pants for lightest warm weather combo.
Tops: Ex Officio Airstrip Lite button down shirt (summer day hikes), Montane Areo wind shirt.
Wind protection: Montane Areo top and Golite Whim bottoms
Rain gear: SMD Gatewood Cape Shelter, Marmot Precip jacket and pants.
Gloves: Pearl Izumi bike gloves (great with trekking poles), Mountain Hardwear Tempest, Patagonia Capilene liners.
Hats: OR Peruvian Windstopper fleece, fleece beanie, Tilley T5, Orvis sun hat.
Sunglasses: Bolle PC with Croakie retainer
Bug control: bug headnet used with wide brim hat (and chemicals), long lightweght clothing (Ex Officio, REI Sahara, etc).