McDonald’s fans are trying their luck to win a cup of gold.   In honor of the shake’s 50th anniversary, McDonald’s is holding a contest where someone will win an 18-karat gold Shamrock Shake cup with 50 emeralds and white diamonds on it.  The cup is worth $90,000.   You’ll be entered to win it every time you buy one of the shakes through the McDonald’s app. And if you need the cup, they’re also auctioning one off on eBay for charity.  The price is up to $30,000 right now.   The auction runs through March 6th and benefits Ronald McDonald House Charities.