What are you feeding your dog?

I have a senior dog that’s been sick the past couple of days. Im not sure if he got into to something, was bit or what. He hasn’t been eating or drinking. I went and got a small bag of blue buffalo and he gobbled it right down. Honestly started getting a little pep back. Not sure I want to go down the path of $45 for a 30# bag of dog food but he’s not eaten puriana well in quite some time.