It's certainly reason to celebrate. And cookies do sound yummy right about now. Maybe I should make some for consolation for myself for not having a full brooder yet.
He's fine. He only ate about 1 cup of M&Ms, so it was below a toxic dose. I keep activated charcoal on hand (this isn't my first bad dog!) for this sort of thing, so I gave that to him right away, too. I took him in to the vet just to make sure he was OK. He's only 6 months old.