I pretty satisfied with my layering system as it gets me through major shifts in temperatures during the spring and fall.
I'm currently using a silnylon Equinox anorak as a waterproof outershell...really compacts down well, but not the best choice with high humidity.
Depending on the activity and distance, I'll be sporting a Swanndri wool shirt or Polartec fleece top.
As a versatile mid-lay, I picked up an Ice Breaker light-weight wool hoodie last spring. What a great piece of clothing!
For ventilation adjustment and when I need long sleeves with adjustable temperatures, but still give me quick drying, I rely on synthetic, long sleeve button shirts. Columbia and 5.11 are my most used tops. If my T-shirt gets soaked or it's just too hot for the base-layer T-shirt, I can wear as a stand-alone.
For a base layer, I typically go with a synthetic T-shirt or tank top. I will say if it's cold and dry, I really like wool T-shirts (Smartwool, Icebreaker, Ibex).
During the summer, I use shorts and convertible pants the most. As the season shifts, I'll go with dedicated pants. Current go-to pants are 5.11 Versa-Tac or Craghopper cargo pants. Undershorts are the very effective Ex Officio mesh variety...good comfort and fast drying.
Of course wool socks and even if in Chaco's and it's cold, I'll still be looking like a goober with wool socks
The Buff/Recon Wrap neck gaiter is always in the pocket and a pair of thin glove liners isnt too far. Even if I'm wearing my Filson packer hat or a synthetic ball cap for lighter treks, I always have a fleece watch cap.
For overnight/backpacking, I have a mini-compression bag (compresses down to the size of a softball) that holds a spare pair of wool socks, Smartwool zip-neck thermal top and Polartec silk-weight long underwear. This is typically my cold-weather sleeping gear and if needed, additional layering. If I'm planning on being around water or expect to get wet with cold weather, I'll add in a pair of Ex-Officio amphi pants...they compact down well and are good in/around water or when needing to dry out my primary pants.
If it's really cold (not as bad as I'm use to down here in GA except up in the mountains), I'll upgrade to a Gore-Tex parka and ECWCS pants.
Layering is critical, especially if the temperatures or your activities vary widely. I am more than comfortable hiking in shorts and a light top with temperatures in the 30-40's, but when you stop to take a break, you really need the ability to regulate body heat and perspiration. Layering makes that so much easier and gives you so many more options.
ROCK6