In my library show this summer (which is actually my school assembly show) I do a bit with handcuffs. The handcuffs are jump cuffs with and additional gimmick that I added.
If you don’t know, jump cuffs you can show that they work, but you can instantly get out of them. They’re 99.9% effective, but there’s still a .01% that something funky could happen. Because of this very small percentage of risk, I keep a set of handcuff keys in my case.
In my routine, the cuffs aren’t part of the escape, they’re a surprise, but I need to get in and out of them quickly. No one knows they’re there until you see them, so the keys never need to be part of the routine like they would if I was escaping from the handcuff and they were the focal point of the routine.
The chances of me not being able to unlock them is insanely low, but keeping the set of keys is insurance. also the keys take up virtually no space in my case, so it’s not a big deal to haul them around.
This is a good example of what can go wrong in a trick and what would you do.