The postal service at one point had a 2" thick 8x11ish envelope that boldly exclaimed "Any weight, anywhere in the US, First class only $x", which wasn't that much. I strongly considered buying a roll of lead, hammering it to fit the envelope and mailing it to unsuspecting people in Hawaii.

I did not only because the package, being lined with lead and thus impervious to x-rays, would panic any of their bomb-detecting people and I really didn't want to get arrested.