I had a narrow miss last summer when we landed in Halifax with some leftover food we'd bought for breakfast that morning. I made a kind of vague declaration about the food we had, but didn't specifically mention the two slices of ham that nobody got around to eating. I knew I had it, but giving a complete itemized list seemed too complicated, and the tiny bit of ham didn't seem important enough to explicitly mention. A dog picked it up at baggage claim. My husband told them we'd mentioned it at immigration, which wasn't strictly true but also wasn't quite a lie. I don't think they believed him, but they just warned us of the fine for failure to declare, which IIRC was several thousand dollars, and of course took the ham.
On another occasion, years ago, we were driving across the border and when I declared my half-eaten sandwich from Subway (which also contained sandwich meat), the agent literally laughed at me. So apparently the importance of this varies depending on the day.