Beginners Guide to riding Fixed/Single Speed in London

One other thing we should add that I would not mind knowing myself: What basic mechanics book is best? I've heard something about zinn or zen?

I've got 'Zinn and the art of road bike maintainance' and really like it. I've built my bike + wheels using it.

My biggest problem with messenger bags if seeing how you can do decent speed on them up big hills.

Try riding a bike, they have far superior climbing abilities then bags ;)

Seriously though as a cyclist/ runner I'll keep my running bag for running and my bike bag for cycling.

Running bags are designed to resist bounce, but not big changes in direction. They are also designed to sit nicely on your back when standing, not leaning over in a cycling position.

Cycling bags would pressumably bounce a bit if you ran with them, but withstand sharp movements better. My bike rucksack is designed to match the curve of your back while in the leaning position.

As for messenger bags. I dont own one, as (most of time) I have no need to access the contents of my bag untill I reach my destination. But it strikes me as a tricky thing, to produce a bag you can easily access, yet will behave itself while your're cycling. So I think they are probably worth spending a bit extra on.