In 1988 I had been renting a cabin in northern California, later visiting and buying a piece of property in Olympia, WA. On my way back to MN I decided to take a scenic Canadian route. Everything was routine at the border until the girl pulled out a roll of toilet paper I had in my trunk (the spare from my cabin stay... I figured, why leave it behind?) She questioned me about it and didn't like my innocent, true answer.
Out of the car, waited until she and a co-worker thoroughly went through everything in my car. I suppose they thought I was planning some back woods survivalist-type escape into the great northwestern wilderness. After all, this was the 1980s and Canadians were using toilet paper by then...
I'm sure they have a lengthy list of items that trigger the full search.