That would imply that they're not taking trial exams seriously enough. I try to treat every trial exam like the real exam.
I've had a cheat sheet ready before I started trial exams. I did the first few exams without a cheatsheet though.
After every exam (or whenever I feel like it), I delete or add stuff to it. It should be a document that you're constantly refining.
If you haven't used your cheatsheet that much, how can you decide what you need on there? You find out what you don't know with every trial exam. You find out what you need to constantly reference (e.g. formulas, diagram of the EMR spectrum etc.) during exams. You find out what parts of the cheatsheet you don't look at all during exams. You probably will end up not needing a cheatsheet, but there is stuff not worth memorising (since you can just look them up).
I try to keep my cheatsheet simple though. I don't want unnecessary information on there (though kudos to those who put in the effort to make an awesome cheatsheet) I find I don't need to reference my cheatsheet a lot, because I find that I know what to do. I also don't put too much time and effort into mine either.
I posted it in another thread if you want to see what it currently looks like (haven't changed it from that yet, there's a a bit of stuff I need to add on and take off from there).
Also, if it's the day before the exam and you still don't know everything you need to know, you really need to ask yourself what on earth have you been doing for the past couple of months. Clearly, you haven't been studying very effectively (unless you were intentionally winging the exam/neglecting physics).
oops, sorry, I kind of went off on a rant.