The Dilemma of Packing Light

As it's now only 4 days until we set off my thoughts turn to what to take with me (although truth be told I started thinking about this some weeks ago).

I've got a pair of rather nice Ortlieb panniers and it's very tempting as with any journey to just fill them up and go. But on the other hand I will be riding a bike for a whole week and any extra weight just means more effort.

Thus the process begins - how many pairs of socks do I really need for one week? Can I get away without taking a hairbrush and how much weight will that actually save me? Shall I just take shorts and hope for the best?

Essentially it's a balance between comfort on the bike (the smallest load possible) vs off the bike (spare clothes, home comforts etc.). To be honest the former normally wins - just the thought of those hills is enough to make me put that 2nd jumper back.