I travelled quite light, although I could have economised more, and the bike itself isn't the lightest. But, for interest, here's a list of what I carried with me:
2 cycle shirts, one short-sleeved, one long
2 prs cycle chorts
4 prs cotton socks
1 pr cycle shoes, comfortable enough to wear to walk around in, with cleats to fit in my SPD pedals.
1 pr light cotton shorts
1 light cotton t shirt (last two for wearing in the evening)
1 sports vest (base-layer)
1 Berghaus waterproof jacket
1 pr waterproof trousers (only used on day 2)
1 travel towel
1 first aid kit
5 OS road maps (1:250,000)
3 End to End guidebooks (two of them left at Perranporth)
2 novels (only 100 pages read in 12 days)
1 pocket DAB radio
1 mobile phone
Rechargers for above 3 items
4 inner tubes (only one required)
Tools and stuff - WD40, oil, spanners, allen keys
1 heavy duty lock - left in a pub in Cornwall, far too heavy
1 combination lock
Sundry power bars (disposed of after a week)
I tried to wash and dry my clothes at each stop, but that wasn't always possible - often radiators wouldn't be on, and it takes more than 12 hours for cycling clothes to dry, and far more for cotton socks to dry. At one point I had 4 pairs of wet socks.
I had plastic bags to keep the books and maps dry, but not the clothes. The panniers weren't waterproof, and the detachable covers I had pooled water inside their elasticated lining, which made the panniers wet at the bottom anyway. I should have remembered the tip to have plastic bags inside the panniers. It's always good to have, at minimum, a pair of dry socks to change into after several hours of rain.
But apart from the heavy ABUS lock, which was a mistake, I'm happy with the amount of kit I took. Remember that you can always buy anything more you need en route.