They're the boxes for screamingly funny, hilariously awful, but scarily plausible products that don't really exist. The photography, typography and layout of these boxes are perfect. I mean, they look exactly like the cheesiest products you'd buy from TV infomercials.
Anyway, the point is that you put people's real presents inside the empty Prank Pack boxes. Then, when they unwrap their gifts, you get that delicious moment of watching their faces as they struggle to be tactful. They think you've just given them the all-time turkey of presents.
Once they figure out that it's just a satirical prank, there's even more laughter - and then gratitude for the much more thoughtful present you've stashed inside.