Don't forget the paperwork. I carry mine in a waterproof wallet underneath the driver's seat.
> Original V5 document
> Insurance certificate
> Driver's license (obviously!)
> MOT certificate

Do you run without a front number plate? If so, it's worth taking a printout of UK number plate legislation. This is the relevant section and the QR code will take you straight to the .gov web page. May be useful if you're standing on the side of the road arguing the point with an over-enthusiastic gendarme! [Linked Image]

Andy