actually it is their business..remember 9-11?that its none of their business.
or that it's your famous organic banana bread
your homemade cream soda.
home-canned beef stew
some sort of liquid homemade food would be best.
they will ask questions..they are required to do so.
what you tell them then falls back to you should you give them mis-information.
remember they send packages cargo ..while they may be in pressurized cabins or they may be in a cargo hold.
some freezing may occur.
you can check the USPS website for more information.