This reminds me of a little blurb in Colin Fletcher's book "The Complete Walker". It was in the second edition that I have, I don't know about subsequent editions or prior editions.

It was related to those metal 35mm film canisters were used to be able to get (I miss those things!) Someone was on trial after a cop saw a film cannister and called that probable cause to search for drugs. The defendant used Fletcher's book where it pointed out other uses for these cannisters. I believe it was a successful defense, but can't remember.