Great question — answering as the UphillTech team:
If an agent were to ask you "what do you have with you?" then you would have to answer that truthfully. However: I don't believe they ask you that - I've never been asked that in an airport or at the land border. They certainly don't give you a form with room to list everything you have with you. A truthful answer doesn't have to be an fully detailed itemized list. "Clothes, a few electronics, some presents for the people I'm visiting." And if it turns out you forgot your "bathroom bag" in that answer, no harm done (as long as that bag isn't full of cocaine or something.) You would probably irritate them if you said "well, this car for one thing, and also the gas in the gas tank, and...
Full answer by Kate Gregory: https://travel.stackexchange.com/a/188401 (CC BY-SA 4.0).
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