I don't leave ANYTHING behind. I take my van's registration & insurance cards with me - I don't want anyone to know who I am if my car is broken into. I take my keys, wallet, mobile phone. The point is...before you go, slim it all down. Only carry your DL, a credit card and debit card, insurance card, and your car and house keys.
Who leaves a key outside their home?? I've never done that. Then again, I also have had alarm systems for the past decade, so if someone comes in, it is going to go off.
DO NOT leave your garage door opener in your car at a trailhead! All you need is that and the address on your registration and it is the easiest break in of your home.
I've had friends had their cars broken into badly and had to have their keys at home redone due to this. Would you want to go hiking and have a burglar show up at your home, if your wife and kids were home alone?
Seriously. People. Quit feeding crooks! Take your keys, your wallet and phone. When they get rewarded with your ID, they know it is worth it.
On the other hand, if you have never had to deal with criminal ID theft, carry on. I have. Anyone who has hiked with me has seen the laminated paperwork I carry due to this happening to me when I was around 17-18. It is beyond one of the worst things you can have happen to your self.