Rover Rescue foster dogs get Royal Canin, Purina kibble and whatever free stuff like Chef Michel I can get.
Some trainers swear by a raw diet. Like a chicken leg/back. When its raw, they can chew the bones without them splintering and causing gastro problems, be it chicken, pork or beef. And the output is small and literally washes away with rain. I know a foster family that feeds their own dog raw and the diarrhea stopped when they made the switch. If you can find a food store that would donate to you, awesome. Using expired Wags RR at Doms makes clearance meat really cheap.