So in high school, we had TI-84 programmable calculators. Those could be used to store text. The teachers knew about that capability, so when there was a test where we were allowed to use the calculator, they wiped the memory of each one at the start of the test. However, I found that there was an app you could install called “fake”, where you could restore all your saved data after a supposed memory wipe by entering a predefined numerical code. Teachers never knew that method existed. I may or may not have used that functionality a couple times. I don’t feel bad about it, as memorizing some physics formulae would have never been any use for me in my later life anyway.

Don’t know if it counts as cheating, but in uni there were some professors who reused exams all the time. Some students set up a download server where you could download all previous exams and its solutions. Pretty sure the professors knew about it as well, but were still to lazy to come up with new exams I guess. So as we were allowed to bring a hand-written sheet of paper with notes (which is a way better policy than all the memorization in high school), I just had all the solutions on there.