an extra gibbon for good luck
jonty: do you really need to take 8 pens into your exam?  laurence: well you know what they say, an extra gibbon for good luck
"to obtain extra luck by adding an extra item or 'gibbon' to what you already have
"jonty: do you really need to take 8 pens into your exam?  laurence: well you know what they say, an extra gibbon for good luck" What is the definition of "an extra gibbon for good luck"?