It is one of the greatest challenges for an actor: learning all your lines. Whether you are Hamlet and just will not shut up or second spear carrier from the left, you need to be 100% secure in your memorization or else the rest of the production will suffer. If your scene partner doesn't have confidence in you to know the correct line, it can feel like performing the high-wire without a net.
So what do you do when you can't seem to commit your text to memory. Many actors have found creative different ways to find aids for themselves wherever they can create them.
All of us have been lazy and rather than memorizing a letter read on stage have relied on the prop having the accurate text printed on it. No we all know the danger is the prop is misplaced and the unsuspecting actor opens the prop and is in a whole world of trouble.
My high school drama teacher proudly told us of his senior play where he had to tape the lines to a scene on a pizza box because he hadn't bothered to learn them. I know of another high school production where the young man playing Danny in Grease seemed to play the drive in movie scene very nervous and quite as any teenager would behave on a date. When complimented on his performance, however, he confessed that he kept looking away from his scene partner because he was reading his lines off the dash board.
You could also embrace your mental relapses. There is a community theatre production that I recall fondly where the young man playing Motel the tailor in Fiddler on the Roof, during his solo Miracles of Miracles jumped up and instead of singing the next line, exclaimed "I forgot my line!"
So share with us any clever tricks you've used to slip your lines into the actual production because you didn't do the best job you could have at your memorization.