I bought a Decathlon cycle bag for £9.99 on a whim thinking to use it up the front of the seat post as suggested on the packaging but didn't think to measure it first. Needless to say it was too long to fit. Next I tried it as a gas tank but found it to be unstable. Bugger, wasted money I thought but after sitting looking at it with a coffee in hand I decided to try it on my new carbon forks. Initial placings didn't work well because of the severe taper in the fork. I then hit on the idea of using the bar harness strap as the top mounting point which itself goes round an aluminium mounting tube on the top of the forks (the harness and aluminium mounting tube are MYOG, the tube not only acts as a mounting point but pushes the bar bag clear of the head tube to avoid any rubbing). Mounting it this way stopped the bag from wanting to slide down the fork and gave it more stability. Now I was faced with another problem, my bicycle related OCD means I don't like a bike to look unbalanced so I had to go out and buy a second bag for the other side so as to give it symmetry

I am pleased with the result as it gives me an extra 2.8 litres of space (I will only put in lightweight stuff that doesn't mind getting wet like tarp etc), it's stable and I think it looks pretty good.
The forks.

Don't believe it.

Mounted.

With bar bag.

Rear view.

NOTE TO SELF............ "Must rub off the B'Twin moniker to regain symmetry".