Reminder from the DVLA, MOT certificate if it is over 3 years old, money, and insurance certificate having your name and the bike specified on it.
It does say on the reminder what you need.
IF YOU DO NOT HAVE A REMINDER -
read this website and it will tell you what to do depending on the circumstances http://www.direct.gov.uk/en/Motoring/OwningAVehicle/HowToTaxYourVehicle/DG_069680
You will defo need the V5C log book or the part 10 new keeper supplement from the previous owner.