E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
All grist that comes to my mill. All is appropriated that comes to me; all is made use of that comes in my way. Grist is all that quantity of corn which is to be ground or crushed at one time. The phrase means, all that is broughtgood, bad, and indifferent corn, with all refuse and wasteis put into the mill and ground together. (See EMOLUMENT.)
To bring grist to the mill. To supply customers or furnish supplies.