13 June 2013
This phrase is clearly an allusion to odds in a bet—such a sure thing that the speaker is willing to wager real money against pastries—back when doughnuts were worth far less than a dollar. The terms were undoubtedly chosen for alliterative and metaphorical purposes. No one is seriously suggesting that people used to gamble with pastries. The phrase dates to at least 1876 when it appears in the 11 March Daily Nevada State Journal:
Several Benoites took a vantage of the half fare tickets offered to those who were to attend the ball given by the railroad boys at Carson last night, and attended it. It’s dollars to doughnuts all enjoyed themselves.
The form dollars to buttons is also encountered in early texts, bolstering the idea that it is the value of the doughnuts, not anything else, that is key to the metaphor. From George W. Peck’s Peck’s Boss Book of 1884:
It is dollars to buttons that...she will be blown through the roof.
Sources:
ADS-L
Oxford English Dictionary, 2nd ed., 1989.