I do a lot of outdoor stuff like fishing, hunting, diving, etc and when I leave my car I am always trying to figure out what to do with my keys. In the past I had three places I hid the keys but I never felt really comfortable about it. I never liked taking keys with me because I worried too much that I might lose them. I used to be able to take them diving, but now that most keys have electronics attached, it has made it impossible.
I recently discovered the HitchSafe, an attachment that slides into my tow hitch that has a compartment that can hold credit cards, drivers licenses, keys, etc. The hitch has four dials on the drawer allowing you to create a custom unlock combination. And it comes with a cover that conceals the HitchSafe.
I recently bought a second for my wife as she is always getting locked out of her car and so she now keeps her spare key in there. In the past she has tried those magnetic boxes that stick to the underside of the car, but they kept falling off and it was hard for her to find it, let alone reach underneath and grab it.
This is exactly the kind of tool I wish I had thought of.