For what product was the first coupon? When did the first one come out?

1894,Coupons are born! Asa Candler, the druggist who bought the formula for Coca-Cola for $2,300, gives out handwritten tickets for a free glass of his new fountain drink.
Source

I guess that I don't need to ask my next coupon question.

From the same site, which was my source, too -

1895 - C.W. Post distributes the first grocery coupon worth one cent towards his new health cereal, Grape Nuts.
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Good job, Mozart !