"A pair of mandarin oranges" as a homophone of "the gold"
Actually 金 and 柑 are both pronounced gam1 in Cantonese, according to Rita Mei-Wah Choy’s ‘Read and Write Chinese’.

While it may be better to refer to Shantou as Chaozhou (潮州), I think CA55CE37 is onto something here.  Indeed, in chaozhouhua 大橘/桔 (orange) and 大吉 (great luck) are apparently near homophones.  A Thai source I have mentions this as well and asserts that oranges are given out at weddings for this reason.  In Thailand, people from the Chaozhou region are dominant in the Chinese community, as you probably know.  And oranges are given for the New Year holiday too (we live in Bangkok and received two oranges from our Thai-Chinese neighbors just yesterday, as it happens.)  It may be simply that two is an even number and thus auspicious.

So, there are various words for orange/tangerine (there is also 橙) and various rationalizations for giving people fruit during holidays, depending on local dialect and local tradition.  I wouldn’t be surprised to learn of more wordplay of this nature, for instance the link between pomelos and ‘to have’.