This is my first question on Worldbuilding, so hopefully I can get the format and so on correct.
In my world, some characters can "will" what they believe to be true into being. If they believe something with just as much certainty as the sky is blue, then they can unconsciously manifest it to be true. They cannot order things into being, but they can be deceived by objects and tools into willing something into reality.
A great example of what I mean is if I declare I can sneak around silently without believing it, I won't be sneaking all that silently. However, if I pick up some ear muffs and I can't hear myself, I believe I can't be heard, then others won't hear me either. For argument's sake, let's say I'm not too bright (don't take a mile here).
This could be achieved through ear muffs or such- the condition is I have to absolutely believe something in order to make it true. I can't just say "hippity hoppet I want a red rocket" to get a Ferrari in my garage- I have to absolutely believe it's already there to make it so. Say I find the keys to a Ferrari in my hallway, I could believe it's in the garage before I actually go look. Thus, I would will it into existance because the keys are in my house (again, some leeway with intelligence).
So, here's my question:
With early 20th Century technology and magic allowed, what equipment/weapons/trinkets could I have that could convince me I'm a master of stealth?