Probably these things that Tractor Supply Company sells (or similar ones from other sources.)
https://www.tractorsupply.com/tsc/product/tractor-supply-pine-pellet-stall-bedding-40-lb
They look like a bag of pellets (almost like short pieces of pencils or dowels), but they are made of pine...
Maple leaves are fine for chickens.
No need to crunch them up. It is fine to add them whole or in any size pieces. Scratching chickens will tend to break the leaves into smaller pieces over time.