lightest and warmest = down; down is a great choice for non moving activities- glassing, camp, etc- very poor choice for on the move
also not the best choice if it's going to be wet, especially with multi-day trips- the down will lose it loft (and consequently it's warmth)
on the move I always start with very light layers- it can be a little miserable at first, but I've learned to "suffer" just a bit as I get started as I normally will warmup- this prevents frequent stops and getting additional layers damp
in cooler temps I have a mid-layer- almost exclusively a fleece layer, preferably with a hood- this is a layer I can don over my light layer if it's not too cold when glassing, eating a snack- it will also be used if I need a warmer layer on the move
always have an insulating layer in my pack for prolonged stops- again preferably with a hood; what weight and wether down or syn depends on the conditions
always have a rain jacket (except extreme cold)- it keeps layers dry, but also keeps warmth in and wind out
obviously appropriate footwear, headwear and handwear
a three hood morning