like they say.
You need to take the
originals of your registration document V5C and insurance certificate. The ins cert should have (on reverse usually) a statement in various languages that it "takes the place of an international green card".
Suggest you also have a copy of the ins cert and a copy of the relevant page of the V5C showing the keeper/vehicle details which you can hand over in case of an accident. This is not essential but is a good idea.
E111 is available over the counter at the Post Office though the new plastic card versions are now being distributed and I guess you'll have to wait a bit to get that sent. I think they are valid after September (???), hmmm, not sure. Note the E111 is not a substitute for personal travel insurance.
You definitely
should have a GB ident, either a sticker or a Euro type no. plate with the blue symbol. Some countries are stricter than others, Austria for example will issue on the spot fine for not having one, France usually couldn't care less.
You
should have spare bulbs (head, indi, stop/tail is enough realistically), and ideally a First Aid pack (camping/hiking stores have small kits for a few quid). Motorcycles are not (now) required to mask the headlamp beam, though I do usually put a piece of black pvc tape on the relevant area just to avoid annoying anyone (unnecessarily

).