grist for the mill

• grist to the mill (UK), grist to one's mill

grist for the mill (uncountable)

1. (idiomatic) Something that is useful or that creates a favorable opportunity.
   • 2003, Peter Lefcourt, The deal: a novel of Hollywood:

     They were sitting across from each other at the bar as Lionel described his odyssey across the country in a Trailways bus, gathering material, as he put it. It was all grist for the mill, life real and raw out there west of New Jersey.

   • 2005 March 2, Leslie Feinberg, “Even McCarthy was gay baited”, in Workers World‎:

     In 1951, Guy Burgess and Donald Maclean, two gay double-agents working in British intelligence, fled to the Soviet Union. This was grist for the mill, linking homosexuality with communist "treason."

• Often found in the expression it's all grist for the mill and variations thereof.

• food for thought
• more sacks to the mill