Not long ago, I came across an ingenious solution to forgetting stuff that had to go out the door with us: the out basket. Our main entrance is in the kitchen, and I had already hung a row of hooks for our keys behind the door (I think I’m the only one who actually uses it, though). People were always forgetting the library books that needed to be returned or letters that needed to be mailed. Solution: a discreet basket that sits on the kitchen counter right beside the door. In it, I place items that need to go out the door.
For my next trick, I need to train everyone in the house (including myself) to check that basket every time we walk out the door.