+1 for system. My Mrs just puts stuff in random places, she's forever losing her debit card, house keys, car key, phone, purse... If I need my keys I know they will be in 1 of 3 places.
A regular scene when leaving our gaff:
Her: have you got your keys?
Me: Yes, we're going out, why would I not have my keys?
Her: Good, I can't find mine.
Another regular scene, she's had the car for work all week:
Me: Where are the car keys?
Her: You had them last.
Me: No, you've had the car all week, I haven't used it.
And yet when it comes to dates and planning I'm rubbish. I've developed a system though - I ask my wife.
Come to think of it, that sounds like it may be remarkably similar to her system for her keys.