What is the literal, non-interpreted meaning of "unusual punishment" or "unreasonable search"?
Well, "unusual punishment" is more complicated, but an unreasonable search is explicitly defined in the Fourth Amendment:
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
I don't know about you, but that sounds pretty clear to me: probable cause supported by oath or affirmation, and a specific description of the place to be searched, along with the person and things it applies to.
The Founders wanted to be very explicit in this case to exclude the generic "general warrants" that the British had used as tools of oppression, so they required cause and detailed instructions for the target of the warrant.
Now that you've read that, see how much "interpretation" it takes to distort that into allowing government agents to do an invasive search of every single person and every single thing that might go on a plane, with no evidence of wrong-doing or probable cause. Before 9/11, airport security got away with it because (1) it wasn't government agents, but airlines/airports doing the searching, (2) you consented to this search by a private airport security as a condition of doing business, and (3) the search was a minimal "procedural search" where you walked through a metal detector -- they'd need probable cause or sufficient suspicion to search you further or detain you. Nowadays we don't even pretend to adhere to the Constitutional text.