I packed almost nothing and was not upset once. It depends on if you want to eat at nice restaurants, be dressed around new people, etc.
I embraced the biking lifestyle and lived out of essentially two outfits of clothing. Here's my packing list:
Ultralight Touring
If I were to add say, two regular outfits to this kit, I would add two Ortlieb-size panniers. The way it is, I fit everything in a small Jandd frame bag and a single Medium-sized Sea to Summit eVent compression sack.
I would bring a warmer sleeping bag if I were going earlier in the year, too. I did not bring the 20º sleeping bag and I did not miss it. This is from August.
Here's me and my bike:
2012 Northeast Bike Tour (Maine, New Hampshire, Vermont, Massachusetts) by
Max Roman, on Flickr