All Multi's ship with three barrels that fit the bikes original key. They are subsequently used for the OE top box and panniers as they are supplied barrel less. So if you don't have any luggage you should have three barrels still, or just a top box then two barrels etc.
Ah puzzle solved then. I ordered mine with the touring and urban packs so have all three barrels but already placed in the kit!
Spot on psy69, I have the touring model so my spare 3rd barrel was in my instruction/service book folder tucked at the bottom, all good as I'm waiting on my duc top box to arrive.