Held 3-in-1 universal non-magnetic tankbag
In many ways this is a cross between the BMW multivario tankbags and the later R1200 series tankbags. It's very well made and very robust - Held build their bags to last - and it comes with the raincover as well.
The rear baseplate has adjustable straps so it can be fitted to any bike. The map-pocket base component is attached to the baseplate by velcro, and has its own front-facing adjustable straps - these go round the steering head, of course. Each tankbag has its own carry handle and external zipped compartment, and they zip individually or in combination to the map-pocket base to give very adaptable storage. You get to the petrol filler cap either by undoing the front straps and tilting the bag(s) backwards, or unhooking the map-pocket base velcro and tilting the bag(s) forwards.
£30 + P&P UK/Europe (let me know where I'll get the price)
$50 + postage worldwide (likely to be pricey if you want it quickly - much cheaper if you can wait a few weeks)
