Wow, I would love to go on a bike trip (without camping). I should plan on it.
I see you use the Kanga rack, which has been out of stock for almost 2 years.
So I bought the Tern HQ bag. I really like it.
Here it is bulging because I put in some papers, headphones and a compact waterproof jacket. Usually it's just my 13" laptop, a USB cable and a phone.
Tern HQ bag on the Verge X11
Lots of very useful pockets
I ended up buying the Tern Go-To bag when I needed to carry more stuff, but I don't use it much or when the weather is threatening.