I'd feel put upon and uncomfortable to be honest - a churchyard is no place to impose upon someone.

More to the point; we don't know specifically why people attend such places, to presume that it's due to a personal loss isn't wise. Someone could be visiting on behalf of someone else etc so to hand them flowers or notes or whatever would only serve to embarrass them i should think.

Better for acts of kindness to be more impersonal - i agree with an above poster about offering flowers at points around the church and other such ideas.