Audax rides

Wanabe- http://www.discountbicycles.co.uk/biz/product.php?xProd=4827 - That's a good one for the price pretty sure Greenbank or Fixedwheelnut uses it.

Holds 30 litres worth, pretty sure you could pick it up cheaper elsewhere online.
that's the one I've seen before. I'll see if I can get hold of one locally to have a look at -- it has to be the expandable one.

Thinking that PBP is a good idea to do at least once in my cycling life, and there just so happens to be one next year...definitely need to train more / better / harder.