lizards like Chamops, amphibians like Habrosaurus, small mammals, juveniles of various larger dinosaurs, small dinosaurs like birds and alvarezsaurs.
It is also possible it may have taken on slighly larger prey at times, like a sub-adult Leptoceratops gracillis or very young Tyrannosaurus that are alone.
Eggs could have been eaten, if it managed to steal them from nests.
Juvenile Acheroraptors would probably also eat more insects and small mammals/lizards than adults.
Cannibalism occurs in most predators, so expect it to at least sometimes eat other Acheroraptors.