Clothing is heavy. After 12 weeks on the road last summer, I found that I nearly lived in these alone, and really didn't need anything else:
2 short-sleeved wool tops; 1 med-wt long-sleeved wool top (can layer or wear alone); 1 pr cycling shorts; 1 convertible pant (legs roll up to knees); 2 pr underwear; wind-proof vest and rain cover.
Once I reached the city I ditched the cycling shorts and rode in my pants... thanks to the comfort of my Brooks saddle.

The wool shirts are incredible; comfortable, breathable, odor-free, easy to wash, fast to air dry...